Why is everything so fixed to light? A planet can spin and have artificial time, even without light. Light is called day, and darkness is called night. That hardly means that it has to keep happening or that it even happened after the event. The light only lasted for less than a second and then it was dark again. Evening (night/darkness) started the first day, not the light. The earth more than likely started spinning then, but how fast and how long it took to spin is not known. It does not matter even how far away from the sun a planet is, it can still rotate. The earth currently spins at 1000 MPH if you are near the equator that speed is less when you move toward the poles. There was no light, until the 4th day, and it was not because the earth was motionless. It was because the light of the sun had not completely fired up. Personally, if the earth had moved from further out away from the sun, the sun may not have even been the brightest thing in the sky. Jupiter and Saturn may have been the two luminaries, that provided the light during the day and night.
Some speculate that a shock wave from nearby could have caused the nebulae to collapse and caused the sun to start forming. According to Genesis, the "let there be light" part was the beginning of the universe, but most relegate the universe to have had a different start all on it's own. But either way, the sun still went through a period of darkness, after the initial "shock wave". Some people even claim that Uranus and Neptune are not in the right place either. Perhaps they migrated out at the same time the earth was migrating in. Genesis does not name the two luminaries as the sun and moon, because they probably were not the sun and moon. But humans lived on the earth so explaining that the Sun and moon came later would not have made sense. We may have liked to of had that pointed out to us today, but it was not necessary to point that out, then. The Sun just kept getting closer and brighter over a long period of time, until the sun was bright in the sky, and eventually the moon became a satellite, and humans started to use a lunar calendar. The Egyptians used a solar calendar, but it seemed the Mesopotamians used a calendar that was based on Jupiter's orbit. The Hebrews started with a lunar calendar.
The boost in agriculture was probably because the earth was now closer to the sun, was receiving the full benefit of the sun, and it now had the moon as a satellite, and it was the first time there were seasons, and the tidal influence of the moon. Yes the Babylonians tracked the motion of the sun, but not at first. The Mesopotamians before the time of the memorable floods, were using Jupiter as the central object to determine time and calendar. The earth just ended up in an orbit that coincided with Jupiter's 12 month orbital pattern. Using the sun while the earth was migrating, probably never yielded a complete pattern during the migration. The current model has Jupiter migrating, but if that was the case, it would have been hard for the Mesopotamians to use Jupiter as it would have been erratic. By the time the Egyptians started their observations, the sun was becoming more normalized as the earth was now settling into it's current orbit. A migration would also explain why the Babylonians added the sun and moon gods in last. They were not primary during the migration. The other planets were closer and more than likely more impressive looking than they are today being further away from them.