A lot is out there about how long the Israelite's were in Egypt which can be devided into two schools of thought, those for Bishop Ushers 215 model or the Ex 12: model which stays faithful to the 430 years to the very day Ex 12:41 the Israelite's left Egypt.
Historically the dispute goes back a long way at least to the time of Jophesus who advocated the view that the Isarelites were in Canaan before they entered Egypt true enough when taken at face value, but look more closely at what the Bible says about when Jacobs name was changed to Israel and then ask the question is there any evidence in the Bible that Israel was used for the decendent's of Abram, Isaac or Jacob before God changed the name of 97 year old Jacob to Israel? A JW I invited to research this confirmed none could be found so that done it remains to look again at the definitions 'decendents' and 'Israelite's' to further clarify.
The 400 years affliction as in Gen 15: speaks of the decendents of Abram only, nowhere does it say anything about the Israelites, Ex 12: on the other hand refers to the Israelite's who came out of Egypt 430 years to the very day and says nothing about the decendent's of Abram so Ex 12: is referring to 'Israel' the decendent's of Jacob not the decendent's of Abram.
Consider here that Isaac the first born of the line of the promise and a decendent of Abraham, died 180 years of age never having set foot in Egypt, 10 years before 130 year old Jacob/Israel entered to reunite the tribal family's as one people, so by no stretch of the imagination can Isaac be confused with the Israelite's as is so easy to do when the Ex 12: 430 year timeline is tied back to the days of Abraham as is advocated by the Bishop Usher model that argues the Israelite's were only in Egypt 215 years.
Gal 3: can be a problem only when read in isolation of other texts, use the same procedure as you would if someone said there was a contradiction with the gospels saying different things and ask them to read all four gospels to get the full picture, like wise with Gal 3: which appears to be saying, by itself, that there are only 430 years between the circumcision covenant and the law covenant , read Gen 47: and acts 7: to get a more complete picture of what Paul has not said about 130 year old Jacob's entry into Egypt in the second year of famine.
To get the age of Jacob start with 30 year old Josephs age when he stood before the ruler of Egypt and add the 9 year total of 7 years plenty plus two years famine which makes Joseph 39, then take Josephs 39 years off the age of 130 year old Jacob to get 91 the age of Jacob when Joseph is born as Jacob completes his 7 years work with Laban for Rachael.
Jacob then agreed to work on for the beasts and he confirms he had worked a total of 20 years when Laban caught up with him: 7 for Leah, 7 for Rachael, and 6 for the beasts.Gen 31:38-41.
The key question when talking with JW's is how old was Jacob when his name was changed, ask the questions and let them confirm from the book they trust what it really teaches.