Interesting thoughts, OldGenerationDude. I agree that P's creation narrative is dependent on ANE mythological concepts, and it has an internal structure with correspondences between the days in the two halves. I do not agree however that the sequence is non-linear (the days are numbered sequentially), that the correspondences are true doublets in that they describe the "same events". P's statement in Exodus 20:8-11 refers to a sequence of six days of labor in which Yahweh " made the heavens and the earth, the sea, and all that is in them", followed by a day of rest (cf. also Exodus 31:17, "I n six days Yahweh made the heavens and the earth, and on the seventh day he rested and was refreshed "), which is the divine model for the human work week, and parsimony would favor an interpretation of Genesis 1 that similarly has six days of work and one day of rest. The correspondences do not reduce the number of days, or identify the different days with each other, but rather show how God's creative activity was orderly with days 1-3 producing the different domains of the cosmos through division (a theme drawing on ANE concepts) and days 4-6 populating these domains ("all that is in them") in the same order. The division of light and darkness in Day 1 is temporal not spatial, and so what is created in Day 1 is the sequence of day/night (with primeval darkness banished to the night) which in Day 4 is populated with the sun, moon, and stars in order to govern (l e memšeleth) the domains into which they are placed (cf. Psalm 136:7-9, "the sun to govern the day, the moon and stars to govern the night"). These domains of light and darkness exist in their own right, cf. Job 38:12, 19-20: "Have you ever given orders to the morning or shown the dawn its place ... What is the way to the abode of light? And where does darkness reside? Can you take them to their places? Do you know the paths to their dwellings?" The Enuma Elish has a similar concept: first Marduk determines the zones and stations for the months and days of the year and then later he causes the moon to shine and "entrusts" to him the night.
I also disagree that this reading of the narrative would require a waiting of three days before there could be light to separate day from night; what is created in v. 15 are "luminaries" (lim'ôroth) that shine light (leha'îr), but what was produced in v. 3 is light ('ôr) itself. There is no necessary reason why this light must come from a luminary that isn't created until the fourth day. John Day has noted the parallels between P and Psalm 104, and we have in v. 19-20 references to the sun and moon and their role in marking the days and seasons, but light itself is manifestation of Yahweh's glory: "Yahweh wraps himself with light as with a garment; he stretches out the heavens like a tent and lays the beams of his upper chambers on their waters...He set the earth on its foundations; it can never be moved" (v. 2-5). So light itself pre-exists the luminaries, and the domains of day and night (alternating periods of light and darkness) also pre-exist the luminaries. This may seem like an odd concept to us, but it accords well with Hebrew cosmology. The sun shines in the firmament but the firmament itself (the sky) shines with its own light that brightens and then dims each day; the firmament is solid and sparkling like ice (cf. Ezekiel 1:22) and in Psalm 104 we read that God's abode in heaven is above the firmament (cf. also Job 22:12-14, Psalm 29:10, Isaiah 40:22), so it would make sense that the glory of God shines through the sparkling firmament (cf. Job 26:13, "by his breath the skies became luminous"). I notice too that Genesis 1:14 states that the luminaries were placed "in the firmament of heaven" (birqîa` haš šamayim ); if days 1 and 4 represent the "same events" and if they are followed by days 2 and 5, which again represent the "same events" respectively, then we would have the luminaries placed inside a domed firmament that is not made until later. I would rather take the narrative at face value and have a sequence of six days that is structured in the manner described above.
I also cannot see what compels reading the narrative as having numbered half days rather than regular full days. The rhythm of the sequence is one of light and darkness, day and night, and that would necessarily involve full days. You say: " Only half a Hebrew day is mentioned in the first six days, each beginning with 'evening' but instead of ending with the next night they stop halfway at 'morning' ". I don't read the creation narrative this way at all. The work performed each day PRECEDES the evening, and then that evening is followed by morning. The narrative does not instead have (1) evening, (2) work, and then (3) morning; it is (1) work, (2) evening, (3) morning. The narrative is often interpreted to assume that the day begins in the morning instead of the evening, but I do not necessarily think that is the case here. The parallel with the Israelite work week suggests that God performs his creative activities during the daytime: "The sun rises, and they steal away ... then people go their work, to their labor until evening" (Psalm 104:22-23). Each creative act from day 2 onward has the act occurring after morning dawns. And then after the work is performed, evening falls. So that is why the narrative is structured the way it is; the focus is on the creative act which does not occur when the day actually starts in the evening but when it is daytime, when Yahweh labors between morning and evening (the references to evening and morning are thus proleptic). That the day-night sequence first begins in the evening can be seen in what is related about day 1: Yahweh's creative act (declaring "Let there be light") necessarily precedes the shining forth of light, and so takes place prior to the dawn on the first day. Then God continues his work during the daytime by naming the period of light ("Day") in contrast to the preceding period of darkness ("Night"). Then after this first day, God works only in the daytime (between morning and evening).