This is a really fascinating problem. It is intractable, with many chronological and exegetical solutions (aimed at harmonizing the various texts into a single harmonistic system) proposed over the centuries but none succeeding completely. This is due in large part to the heterogenous material found in the OT and the intrabiblical exegesis of this material in the NT, which has imposed on the OT texts some interpretations that now have scriptural authority by virtue of their inclusion in the NT.
Here is a detailed survey of the texts and subsequent interpretations up to the rabbinical period:
Stage 1: The sojourn-exodus narratives without a chronological framework
JE (before the exilic period): The early preexilic narratives of J and E lack any specific chronological data about the length of time of the sojourns in Canaan and Egypt. The amount of time involved is unspecified. It covers a period of several generations but the number of generations is given only in P. The genealogical materials collected in 1 Chronicles show that the number of generations covered in the Egyptian sojourn varied considerably in the traditions. Thus there are 4 generations from Levi to Phinehas in 6:1-4, 5 generations from Judah to Nahshon in 2:1-20, 6 generations from Judah to Bezaleel in the same passage, and 10 generations from Joseph to Joshua in 7:20-27 (Phinehas, Nahshon, Bezaleel, and Joshua are all contemporaries in the wilderness narratives).
Stage 2: The development of a Zadokite chronographical framework
P (during the exilic period): The priestly code, on the other hand, was responsible for the notices in Exodus 12:40 and the genealogy in 6:13-27, as well as all the many detailed lists in Genesis with age information. The priestly author was strongly interested in indicating the passage of time in a precise manner. The chronological notice in 12:40 (as given in 4QExod c and the MT) simply states that "the length of time the Israelite people lived in Egypt was 430 years". This number however fits together with P's overall numerical scheme, which is based on the numbers 360 and 70. P follows a schematic calendar which has 360 days in a year (as it is in P's Flood narrative in Genesis), and 70 reflects the priestly interest in sabbatical weeks (as in Leviticus 25). So according to P, the period between the birth of Arpachshad and the birth of Terah was 220 years, and the period from the birth of Arpachshad to Abraham's 70th year was 360 years (220 + 70 + 70 = 360). Another two cycles of 70 years brings us to the death of Shem (360 + 70 + 70 = 500). From Abraham's 70th year to the beginning of the sojourn in Egypt is another 220 years (30 years to the birth of Isaac, 60 years to the birth of Jacob, and 130 years until Jacob's descent into Egypt). Then it is another 70 years until Joseph's death (Genesis 50:22, 26), yielding another period of 360 years between Abraham's 70th year until the death of Joseph. The 430 years of the sojourn is part of this numerical plan as it is the sum of 360 + 70. That remainder of 70 is, of course, the first 70 years of the sojourn before the death of Joseph. The longer segment then corresponds to the period of Israelite slavery. So we have a period of 360 years from the birth of Arpachshad to Abraham's 70th year, then 360 years to the death of Joseph, and then a final 360 years of slavery to the exodus. This is the rather deliberate periodization scheme of P.
But as mentioned in the OP, the numbers given in the genealogy in ch. 6 (also by P) appear to be inconsistent with this, yielding a time span much shorter than 430 years. However this inconsistency depends on Genesis 46:11 which lists Kohath among the 70 (notice that number again) "members of Jacob's family" (46:27). This list is also by P (compare Exodus 1:1-5) but it clearly has been reworked by the Pentateuch redactor to harmonize with the Joseph narrative from JE. So the list also contains the names of Er and Onan (Genesis 46:12) who certainly could not have entered into Egypt, and so there is an awkward harmonizing gloss that notes that they had already "died in the land of Canaan". Similarly, ten sons are listed for Benjamin (v. 21), whereas in the Joseph narrative he is still a boy (43:8). And again it lists Manasseh and Ephraim as the two sons of Joseph born in Egypt (v. 20), so again these are not those who were born in Canaan and moved to Egypt. So most scholars believe that this list originally wasn't an ennumeration of those who went into Egypt, but simply "a list of Jacob's sons and grandsons, originally compiled without reference to the migration to Egypt" (Skinner, p. 493). So it is doubtful that Kohath in the genealogy in Exodus 6 was necessarily conceptualized in P as born in Canaan rather than Egypt. The genealogy only gives ages at death rather than the age at the birth of one's son (as is the case in Genesis), so it is not concerned with demarcating the limits of the Egyptian sojourn. The numerical plan is rather to have Aaron and his Levite forbears live a total of 490 years prior to the exodus (137 + 133 + 137 + 83 = 490), which is 7 x 70. This is a significant time span in later periodizations of history (cf. Daniel 9 and its subsequent use in the Apocalypse of Weeks, the Dead Sea Scrolls and the Testament of Levi), as it is equivalent to ten jubilees (the jubilee is also unique to P, see Leviticus 25). Of course this total also exceeds the 430 years, which leaves some room for overlap between generations and Levi's early life in Canaan, but probably not enough if one looks too closely.
Stage 3: Addition of a new chronographical datum
R (early post-exilic period): The redactor responsible for the present form of the Pentateuch (Ezra?) added a new statement about the length of time the Israelites were enslaved in Egypt. This was in the interpolation of v. 12-16 into ch. 15, the JE account of covenant God made with Abraham (P's account of the covenant is in ch. 17). This passage adds a dream vision aimed at explaining why the covenant blessing does not start right away but only a lengthy period of sojourning and slavery in a foreign land (something not mentioned in P's rather rosy account of the promise). The secondary nature of the passage is indicated by several features, including the fact that it presupposes the promise not made until v. 18, the double reference to darkness falling (which is peculiar since the reference in v. 17 of darkness falling at dusk follows the description of "a thick and dreadful darkness" falling before the sun had set in v. 16), and the fact that Abraham is not described as awakening from his sleep. This passage states: "Know for certain that your descendants will be strangers in a country not their own, and they will be enslaved and mistreated for 400 years...In the fourth generation your descendants will come back here" (Genesis 15:13, 16). This comment from R is exegetical on the material in P without sharing P's chronographical framework. The four generations are those presumed in Exodus 6 (Levi < Kohath < Amram < Aaron) and the 400 years is somewhat parallel but identical to the 430 years of Exodus 12:40. Unlike many later interpreters, R has read P as designating a lengthy Egyptian sojourn. But the 30-year difference between the two figures will constitute grist for the chronographical mill in the later Hellenistic era.
Stage 4: Midrashic chronographical interpretation
In the early Hellenistic era, interpreters began to shorten the length of the sojourn to somewhere between 210-240 years. The motivation for this was probably due in part to the exegetical problem raised by the juxtaposition of Genesis 46:11 (which in its present form does construe Kohath as born in Canaan) with Exodus 6. A wide variety of different solutions were adopted.
Testament of Levi (third century BC). This is an Aramaic testament attributed to Levi, as preserved in 4QTestLevi and Cairo Genizah fragments; a later version composed in Greek forms a part of the Testaments of the Twelve Patriarchs (first century BC). This document gives a biographical narrative of Levi's life and works through the problem posed by Kohath in Exodus 6. According to this early pre-Maccabean text, Kohath was born when Levi was 34 years old (Aramaic Levi 11:5-7), and then Levi entered Egypt when he was 48 (Aramaic Levi 12:8). This follows the present text in Genesis which implicitly has Kohath born in Canaan. Then Levi lived another 89 years in Egypt before he died, giving a total of 137 years as it is in Exodus 6:16. The chronology is similar but slightly different in the Greek Testament of Levi: Kohath was born when Levi was 35 and Levi entered Egypt when he was 40 (Testament of Levi 11:4, 12:5), with Levi living 97 years in Egypt. Aramaic Levi also states that Amram was born when Levi was 64 and Amram married Jochebed when Levi was 94 (Aramaic Levi 11:11, 12:5). Here the text in the Greek testament is identical: "Jochebed was born in the sixty-fourth year in Egypt... And in my ninety-fourth year Amram took Jochebed my daughter to him to be his wife, as they were born in the same day" (Testament of Levi 11:8, 12:4). One final datum relevant to the chronology in the Pentateuch is the statement that Joseph died when Levi was 118 years old (Aramaic Levi 13:1; cf. Testament of Levi 12:7). This would have Joseph live 70 years in Egypt after the start of the sojourn (48 + 70 = 118).
These biographical details show that the author of the Testament of Levi construed the sojourn in Egypt as quite short; Levi's own lifetime extended some 43 years into the marriage of Amram and Jochebed. So Levi lived 48 years in Canaan, then he lived 16 years when Kohath became father to Amram, and then another 30 years before Amram married Jochebed. Adding this with the 83 years of Aaron's life, this yields a minimum of 129 years (16 + 30 + 83) for the sojourn, and since Amram presumbly died prior to the exodus, the sojourn had to have been at least 153 years (16 + 137). If Aaron was born in Amram's last year of life, the sojourn could not have been longer than 236 years. So the author clearly splits the 430 years between sojourns in Canaan and Egypt. Unfortunately the author of the Testament of Levi did not state how old Amram was when he became father to Aaron or Moses, but a later text (4Q559) indicates that he was 110 years old when he fathered Aaron. If the author of Levi had a similar age in mind, then the length of the sojourn in Egypt would equal about 210 years (16 + 110 + 83), suggesting a split of 220 years in Canaan and 210 in Egypt. This is the solution found in Pseudo-Philo and other writers.
LXX and the Samaritan Pentateuch (mid-third century BC). The Hebrew text in Exodus 12:40 is incompatible with a short Egyptian sojourn, so the text of both was modified via later redaction:4QExod c and MT: "Now the sojourn of the children of Israel when they dwelt in the land of Egypt was 430 years"LXX: "Now the sojourn of the children of Israel when they dwelt in the land of Egypt and in the land of Canaan was 430 years"SP: "Now the sojourn of the children of Israel and their fathers when they dwelt in the land of Canaan and in the land of Egypt was 430 years".
The LXX solves the problem posed by Genesis 46:11 by extending the period of 430 years into the time when the sons of Jacob lived in Canaan. Notice that the gloss referring to the "land of Canaan" occurs in different locations in the LXX and SP versions; this "floating" quality is characteristic of secondary accretions. Although this solved the discrepancy posed by Genesis 46:11, it left the period of the Egyptian sojourn now undefined. Hellenistic chronographers wanted to define the period of the sojourn more precisely and most solutions pushed about half of the 430 years into the period prior to the sojourn. The problem with this however is that the wording in the LXX can carry this only as early as the birth of Jacob's first sons. If the 430 years are to be pushed as far back as Abraham (such as to the covenant or the birth or weaning of Isaac), it is not possible to construe Abraham or Isaac as among the "children of Israel". So the SP contains an additional accretion that adds the words "and their fathers" to enable this interpretation more felicitously.
Demetrius(late third century BC). This is the earliest explicit division of the 430 years into two defined periods, and the first to divide them evenly into periods of 215 years each:"And they lived in the land of Canaan from the time when Abraham was chosen from among the gentiles and migrated to Canaan: Abraham for 25 years; Isaac, 60 years; Jacob, 130 years. All the years in the land of Canaan were thus 215....From Adam until Joseph's brothers came into Egypt there were 3,624 years; and from the deluge until Jacob's coming into Egypt , 1,360 years; and from the time when Abraham was chosen from among the gentiles and came from Haran into Canaan until Jacob and his family came into Egypt there were 215 years" (Demetrius, Fragment 2; quoted in Eusebius, Preparatio Evangelica 9.21.16, 18)
This interpretation draws on the figures in the LXX (e.g. 3,624 years instead of the 2,248 of the MT and 1,360 years instead of the 580 of the MT) and reckons the 215 years in Canaan as commencing with Abraham's departure from Haran (according to Genesis there were 25 years from this event to the birth of Isaac and then 60 years to the birth of Jacob and Jacob was 130 years old when he migrated to Canaan). Although not explicit, this scenario also makes the 400 years of Genesis 15:13 start when Isaac was 5 years old (25 + 5 = 30), a datum critical to the interpretation that reckons the 400 years as starting with the weaning of Isaac. It is clear however that starting the 400 years prior to the Egyptian sojourn is not presumed in Genesis 15:13. Although Canaan could be regarded as "a land not their own", the latter reference contrasts with Canaan since after the 400 years in "a land not their own" Abraham's descendents would be brought back "here" (i.e. Canaan); it is thus a departure of the sense of the original text to construe the 400 years as split between Canaan and Egypt.
Then in an intra-sojourn chronology somewhat resembling that of the Aramaic Testament of Levi, Demetrius gives the length of the period of the sojourn itself. First he states that Levi lived on in Egypt for 17 years before begetting Kohath at age 60 (9.21.19). This notably posits Kohath as Egyptian-born, rather than born in Canaan. Then "when Kohath was 40 years old he begat Amram who was 14 years old when Joseph died in Egypt at the age of 110; and Kohath was 133 years old when he died. Amram took as his wife his uncle's daughter Jochebed and when he was 75 years old he begat Aaron. But when he begat Moses Amram was 78 years old, and Amram was 136 years old when he died". The sum of these numbers (17 + 40 + 75 + 83) gives the length of the Egyptian sojourn as 215 years.
Apocalypse of Weeks (early second century BC). This is an important proto-Essene apocalyptic "survey of history" preserved in the Epistle of Enoch (1 Enoch 93:1-10, 91:11-17). It anticipates many ideas found later in Jubilees and it organizes history in "weeks" each consisting of 490 years (= ten jubilees or seventy sabbatical weeks), with significant events sometimes occurring at the close of the 490-year cycle. So within the first week, the Flood is supposed to come and the Noachian laws given, and this would correspond to the 490 years spanning between 981-1470 AM (i.e. years from the creation of Adam). Then at the close of the third week would come the covenant made with Abraham, and this corresponds to the 490 years spanning between 1471-1960 AM. And then at the end of the fourth week would come the covenant made with Moses and the tabernacle in the wilderness, and this corresponds to the 490 years spanning between 1961-2450 AM. All of this adheres very closely with the jubilees chronology of Jubilees, which dates the Flood to 1308-1309 AM, the migration of Abraham into Canaan to 1953 AM, and the exodus in 2410 AM. This shows that the author of the Apocalypse of Weeks split the 430 years of Exodus 12:40 between the patriarchs' sojourn in Canaan and the sojourn in Egypt and employed the same jubilees framework as Jubilees. The motivation for this chronology will be explained more in the discussion on Jubilees.
Jubilees (mid-second century BC). Jubilees employs its own detailed idiosyncratic chronology of the patriarchal period while following the SP reckoning of the 430 years. But it starts the 430 years with the birth and circumcision of Isaac, regarded by the author as the "first" under the covenant (Jubilees 15:1, 16:13-15). This event is dated to "the fifth year of the fourth week of the forty-first jubilee", whereas "Israel entered into the land of Goshen on the first of the fourth month in the second year of the third week of the forty-fifth jubilee" (45:1), and the exodus is dated to "the forty-ninth jubilee, one week, and two years" (50:4). In other words, it dates the birth of Isaac to 1980 AM, the migration to Egypt to 2172 AM, and the exodus to 2410 AM. This divides the 430 years as 192 years in Canaan and 238 years in Egypt. The whole chronology is engineered in order to make the entrance of Israel into Canaan occur in 2450 AM (40 years after the exodus in 2410 AM) — the climax of the whole jubilee cycle as it corresponds to the 50th jubilee year, making it a jubilee of jubilees (on the basis of 49-year jubilees). This is the principal reason why a short Egyptian sojourn is preferred by Jubilees; a 430-year sojourn is much too long for the 50th jubilee to fall anywhere significant.
In addition to interpreting the 430 years of Exodus 12:40, Jubilees also gives an implicit reckoning of the 400 years of Genesis 15:13. In between the references to the 400 years and the fourth generation in Genesis 15, Abraham is told that he "will go to your fathers in peace and buried in old age" (v. 15). The reference to "peace" in contrast to the slavery mentioned in v. 13 suggested to the interpreters that the 400 years would have to start after the death of Abraham, as he would have no peace if his children were enslaved (this is very different than the "weaning of Isaac" interpretation of the 400 years, starting it well before Abraham's death). Jubilees dates the death of Abraham to 2050 AM (22:1), exactly 400 years before the entrance of Israel into Canaan in 2450 BC. This reckoning combines the 400 years with the four generations in Genesis 15:13-16, such that the 400 years end when the 4th generation ends (i.e. at the death of Moses just prior to Israel entering into Canaan). Most other interpretations of the 400 years have it end with the exodus, but this is not possible in Jubilees which starts the 400 years much later in the timeline.
4Q252 (first century BC). This reworking of Genesis states: "Terah was 140 years old when he left Ur of the Chaldeans and went to Haran, and Abram was 70 years old. Abram lived five years in Haran, and then he went to the land of Canaan. Sixty five years later [Rebekah left Haran to marry Isaac]" (2:8-10). Abraham's 70th year is an implicit pivot-point in P (it marks the boundary between two periods of 360 years), but nothing is described as happening in that year. 4Q252 assigns an event to that year: Abraham was 70 years old when he left Ur. Since Genesis 12:4 relates that Abraham was 75 years old when he left Haran, this leaves only a 5-year sojourn in Haran. These extra 5 years offer an alternative explanation for the 30-year difference between the 430 and 400 years. Instead of it running from the departure of Abraham from Haran to Isaac's weaning at age 5 (from age 75 to 105 of Abraham's life), it would run from the time Abraham left Ur to the birth of Isaac (from age 70 to 100). This idea would be picked up in later interpretations.
4Q543 (first century BC). The Vision of Amram relates that Amram witnessed a vision "in the one hundred and thirty-sxith year, that is the year of his death, in the one-hundred and fifty-second year of the exile of Israel in Egypt" (1:1-4). This continues the chronology implicit in the Aramaic Testament of Levi. In that text, Levi was 48 when he entered Egypt and Amram was born when Levi was 64, i.e. 16 years later. The addition of this number with the age of Amram at his death gives the length of the sojourn at that moment as 152 years (16 + 136 = 152).
4Q559 (first century BC). This text gives a unified chronology of the period from Abraham to the judges and is aimed at specifying the exact length of time from Abraham to the exodus. The relevant portion here states: "Abraham was 99 years old when he fathered Isaac, Isaac was 60 years old when he fathered Jacob. Jacob was 65 years old when he fathered Levi. He gave to Levi the book of the words of Enoch to preserve and pass on to his own descendants. Levi was 35 years old when he fathered Kohath. Kohath was 29 when he fathered Amram. Amram was 110 when he fathered Aaron. Aaron left Egypt with the priests, who totalled 11,536" (2:3-10). These figures agree with those given in the Testament of Levi, although the reading of some of these is somewhat conjectural. But if the reading is accurate, then this would suggest that 4Q559 presumes a period of 382 years from the birth of Isaac to the exodus (60 + 65 + 35 + 29 + 110 + 83 = 382). This leaves about 18 years unaccounted for with respect to the 400 years. If Abraham was 99 years old when Isaac was born (the MT states his age as 100), then the 400 years began when Abraham was 81. This is within the timeframe between Abraham's departure from Haran at age 75 and the birth of Ishmael at age 86 (cf. Genesis 12:4, 16:16), so the author may well reckon age 81 as the time when God made the covenant with him as related in Genesis 15. This interpretation then starts the 400 years at the time when God gave the prophecy of the 400 years.
The Assumption of Moses (early first century AD). This is the book that is alluded to in v. 9 of the epistle of Jude. It purports to relate the testament that Moses gave to Joshua in his 120th year "which is the two thousand five-hundredth year since the creation of the earth" (1:2). It thus dates the entrance of the Israelites into Canaan under Joshua to 2500 AM. This date also corresponds to the 50th jubilee, the jubilee of jubilees, if the length of each jubilee is reckoned as 50 instead of 49 years. It is thus unique for computing jubilees in such a manner, but it otherwise seems to agree with Jubilees in making the 50th jubilee fall on the same event. This suggests that like Jubilees, the author of the Assumption of Moses also split the 430-year sojourn between sojourns in Canaan and Egypt. That the author reckoned Moses' death as marking a key moment in world history is confirmed in the statement in 10:12 that "there will be 250 times from my death, my being taken away, until [the Lord's] advent". Although the length of a "time" is not stated, it may well be a sabbatical week, or 7 years, such that there would be 1,750 years or 35 jubilees from the death of Moses (2500 AM) until the end of the world. The apocalyptic survey of history given in ch. 2-10, with its references to King Herod, suggests that the author did not view the end as that far off from his time. One may compare with the concept in the Book of Watchers in 1 Enoch that 70 generations would pass from Enoch to Judgment Day (1 Enoch 10:11-12; cf. Luke 3:23-37 which computes 70 generations from Enoch to Jesus).
Pseudo-Philo (early first century AD): The author embeds his interpretation of the 430 and 400 years in a speech given by Amram, the father of Moses, to the Israelites desiring to divorce their wives to prevent a slaughter of the innocents (the two themes are again combined in the Matthean nativity narrative, which draws heavily on Mosaic traditions). Amram points out that their misfortune was prophesied in advance to Abraham but it accompanies the promise that the nation of Israel would not sink into oblivion:"There will be fulfilled the covenant that God established with Abraham when he said, 'Indeed your sons will dwell in a land not their own and will be brought into bondage and afflicted 400 years.' And behold from the time when the word of God was spoken to Abraham, there are 350 years; from the time when we became slaves in Egypt, there are 130 years. Now therefore I will not abide by what you decree, but I will go in and take my wife and produce sons so that we may be made many on the earth" (Pseudo-Philo 9:3-4).
Here the author clearly divides the 430 and 400 years between Canaan and Egypt, as does the LXX. The author reckons 220 years in between the giving of the covenant to Abraham to the moment when the Israelites became slaves in Egypt (350 - 130 = 220), and then 130 years of slavery to the "present". Since the birth of Moses was to follow, and the exodus would occur 80 years later, the 430 years of Exodus 12:40 is thereby accounted for (220 + 130 + 80 = 430). This periodization thus splits the 430 years into 220 years in Canaan and 210 years in Egypt (cf. Pseudo-Philo 8:8 which states explicitly that the Israelites dwelt in Egypt for 210 years). This differs from the even 215 - 215 division found in Demetrius. The chronographical system however is altogether different. Demetrius reckoned the 430 years as starting when Abraham left Haran and 5 years earlier (which would be the case if 220 years instead of 215 years are placed prior to Egyptian sojourn) would put the start of the 430 years to Abraham's 70th year which 4Q252 posits as the time when Abraham left Ur. But Pseudo-Philo does not reckon the start of the 220 years from Abraham's 70th year (which incidentally is the span presumed in P, 220 years from Abraham's 70th year to the beginning of the sojourn). For him the 430 years begins explicitly with the giving of the covenant to Abraham; while P's account of the covenant is dated to the 99th year of Abraham, the version in Genesis 15 is undated but is to be located sometime between Abraham's 75th year (when he left Haran) and his 86th year (when Ishmael was born, cf. 12:4, 16:16). Jubilees dates the vision to when Abraham was 84 (14:1), and 1QapGen dates it to when Abraham was 85 (22:27-29). So either Pseudo-Philo is using a different chronographical system (as did the author of Jubilees), or he didn't work out the chronology. The simplest solution is that the author confused the 430 years with the 400 years. Another problem is Pseudo-Philo's handling of the 130 years of slavery; this construes the whole period of the Egyptian sojourn as a period of slavery, forgetting about the 70 years of peaceful living prior to the death of Joseph. This indicates again that Pseudo-Philo was unsuccessful in developing a consistent system.
Galatians 3:16-18 (mid-first century AD). The apostle Paul wrote: "The promises were spoken to Abraham and to his seed...The law, introduced 430 years later, does not set aside the covenant previously established by God and thus do away with the promise. For if the inheritance depends on the law, then it no longer depends on a promise; but God in his grace gave it to Abraham through a promise". This presents an interpretation of Exodus 12:40 that follows the majority opinion of the day: the 430 years are to be split between sojourns in Canaan and Egypt, with the era beginning with the covenant promise made with Abraham. So Demetrius reckoned 215 years of sojourn in Canaan starting with Abraham's departure from Haran and Pseudo-Philo starts the 430 years with the covenant made with Abraham, although his chronography does not work sucessfully. 4Q559 starts the 400 years from the time God gave the promise in Genesis 15, so the author probably intends to start the 430 years sometime prior to Abraham's migration from Haran unless it is meant to end with the death of Moses and the conquest of Canaan. Jubilees starts the 430 years with the birth of Isaac, quite some time after JE's version of the promise but very close to P's (which was dated by P to Abraham's 99th year). We don't know what theory Paul had on subdividing the 430 years, or which promising event he had in mind. But thanks to Paul and the canonization of his letters as scripture, Christianity inherited the post-exilic midrashic interpretations of Exodus 12:40, which have overridden what is actually stated in that text.
Josephus (late first century AD). The famed historian actually gives several different reckonings. He first characterizes the length of slavery in Egypt in agreement with Genesis 15:13: "For four hundred years they lived under these oppressions and strove against each other, the Egyptians desiring to destroy the Israelites (Antiquitates 2.204)". But a few chapters later Josephus indicated a much shorter length of the sojourn in agreement with the periodization of Demetrius: "They left Egypt in the month Xanthicus, on the 15th day of the lunar month, 430 years after our forefather Abraham came into Canaan, but only 215 years after Jacob migrated into Egypt" (2.318). So here he splits the era into two periods of 215 years, the first beginning with Abraham's departure from Haran.
Acts 13:17-20 (late first century AD or early second century AD). The book of Acts quotes Genesis 15:13 in a passage that implies an Egyptian slavery of 400 years (7:6-7). But the author construes the 400 years as split between sojourns in Canaan and Egypt: "The God of the people of Israel chose our fathers; he made the people prosper during their stay in Egypt, with mighty power he led them out of that country, he endured their conduct for about forty years in the desert, he overthrew seven nations in Canaan and gave their land to his people as their inheritance. All this took about 450 years. After this, God gave them judges until the time of Samuel the prophet". The figure "about 450 years" is clearly an approximation but fits very well with the Demetrius' reckoning that construes the 400 years as spanning between the fifth year of Isaac (when he was weaned) to the exodus. Then the 40 years in the wilderness and 5 years in the conquest of Canaan (cf. Joshua 14:10) would span an additional 45 years, leaving 5 years for the span between the birth of Isaac and his fifth year. So Acts 13:17-20 likely has in mind the "choosing" of Abraham in his 99th year (P's account of the covenant), one year before the birth of Isaac. So the author probably has 451 years in mind, i.e. "about 450 years".
Seder Olam Rabbah (second century AD). This rabbinical chronographic work reckons the 400 years from the birth of Isaac: "It was said to our forefather Abraham at the covenant between the pieces: 'You shall certainly know that your seed will be strangers in a foreign land for 400 years.' Who is that seed? That is Isaac, of whom it is said: 'Because Isaac will be called seed for you.' About Isaac it says: 'Isaac was 60 years of age when they were born.' Our forefather Jacob said to Pharaoh: 'The days of the years of my wandering are 130 years.' This makes together 190 years, this leaves 210 years, a sign for the lifetime of Job who was born at that time as it is said: 'Job lived thereafter 140 years' and it is said: 'The Eternal added double to all that Job had.' It turns out that Job was born when Israel migrated into Egypt and died when they left" (Seder Olam Rabbah, 3). Here the author starts the 400 years with the birth of Isaac (not his weaning at age 5, as others have done). The first segment is 60 years to the birth of Jacob, and then 130 years to the migration of Jacob into Egypt. The remainder is 210 years, which corresponds to the period of the sojourn in Egypt. The rabbi here takes a creative reading of Job to support this: Job lived 140 years after his trial (42:16), and the adding double to all Job had is interpreted to mean that Job was 70 years old at his trial and went on to live another 140 years. This gives a total of 210 years for his life. This duration for the sojourn is reinforced in the next section:"Perhaps Israel was in Egypt for the full 400 years. But Kohath was among those who entered Egypt and it is written, 'the years of the life of Kohath were 133 years,' and 'the years of the life of Amram were 137 years.' Together with 80 years of Moses this makes 350 years...From the death of Levi to the exodus were 116 years. The slavery extended not more than that time and not less than 86 years, the age of Miriam at the exodus, since she was named for the bitterness".
This passage starts with the exegetical problem posed by the juxtaposition of Exodus 6 and Genesis 46:11. The solution is to shorten the period of the sojourn; there were only 116 years from the death of Levi to the exodus. This figure was derived by adding the age of Isaac when he fathered Jacob, the number of years from then when Levi was born, and then the number of years to Levi's death (60 + 87 + 137), a total of 284 years. This leaves 116 years to the exodus, completing 400 years. If the Egyptian sojourn lasted 210 years, then the sojourn in Canaan would had to have been 220 years. The same division can be presumed for the Testament of Levi and Pseudo-Philo, in contrast to the even 215/215 split presumed by Demetrius and Josephus.
Seder Olam Rabbah, 1 also reckons the 430 years as commencing in Abraham's 70th year: "Our father Abraham was 48 at the time of the Dispersion....Our father Abraham was 70 years old when he was spoken to at the covenant between the pieces as it is said, 'And it was after 430 years,' etc. After that he was spoken to he went to Haran, stayed there five years as it is said, 'Abram was 75 years old when he left Haran.' It follows then that from the Dispersion until Abraham left Haran there were 26 years." This scenario was anticipated by 4Q252 which has Abraham leaving Ur at age 70 and then living in Haran for 5 years prior to his departure. But innovatively it dates the covenant made in Genesis 15 to Abraham's 70th year. It then explicitly makes the 430 years span betwen Abraham's 70th year and the exodus. This brings us back to the problem raised by Acts 13. The period of "about 450 years" was shown to contain the 400 years spanning between the birth of Isaac when Abraham was 100 and the exodus. The implication of this is that the 430 years begins with the 70th year of Abraham. Interestingly, the author of Acts has a similar scenario to that presumed by 4Q252 and the Seder Olam Rabbah: "The God of glory appeared to our father Abraham while he was still in Mesopotamia, before he lived in Haran. 'Leave your country and your people,' God said, 'and go to the land I will show you.' So he left the land of the Chaldeans and settled in Haran. After the death of his father, God sent him to this land where you are now living" (Acts 7:2-4). This differs from the narrative in Genesis in two ways. There is no divine apperance to Abraham in Ur related in Genesis, and thus no promise made to him at that time. Moreover, the age of Terah's death given by P indicates that Terah was still alive when Abraham left Haran. But here we find a divine promise of land made to Abraham when he still lived in Ur. The timing of Abraham's departure from Ur in 4Q252 reflects the midrashic claim in Acts 7:2-4 that Abraham left Ur after receiving the promise of land.
Subsequent interpretations build on these ideas. The rabbinical chronology of the Talmud (third-fourth century AD) dates the exodus to 2449 or 2450 AM, the 50th jubilee, the jubilee of jubilees (cf. b 'Abodah Zarah 9b, b Yoma 9a, etc.). This is the same date Jubilees assigns to the death of Moses and conquest of Canaan (cf. the similar reckoning in the Assumption of Moses). The Song of Songs Rabbah (sixth century AD) states that Israel was in Egypt for 210 years. The Mekhilta de Rabbi Ishmael interestingly treats the 400 years of slavery as conditional: if Israel repents of its sins, God would deliver the nation after four generations but if not she would stay enslaved for 400 years. This conditional reading thus does not take the 400 years as corresponding to actual events. The Targum Pseudo-Jonathan (tenth century AD) posits 210 years of sojourn in Egypt and notes that this corresponds to 30 sabbatical years (7 x 30) (ad Exodus 12.40). Today the more parsimonious 215/215 split of Demetrius and Josephus is preferred today by Christian interpreters, and a variant of this is adopted by the Watchtower Society today.