Gawd "revealed himself to Moses at the burning bush. From then on Moses was busy communicating Gawd's word to the beleagured jews. When did Moses write Genesis?
3:2 And the angel of the LORD appeared unto him in a flame of fire out of the midst of a bush: and he looked, and, behold, the bush burned with fire, and the bush was not consumed.
3:3 And Moses said, I will now turn aside, and see this great sight, why the bush is not burnt.
3:4 And when the LORD saw that he turned aside to see, God called unto him out of the midst of the bush, and said, Moses, Moses.
3:5 And he said, Draw not nigh hither: put off thy shoes from off thy feet, for the place whereon thou standest is holy ground.
3:6 Moreover he said, I am the God of thy father, the God of Abraham, the God of Isaac, and the God of Jacob. And Moses hid his face; for he was afraid to look upon God.
Based on the above enounter, it is clear that this was the first time that gawd had introduced himself to Moses. Therefore, Moses had not written Genesis prior to this encounter.
Yet, after this encounter, Moses, age 80, is clearly busy getting the jews out of Egypt and writting over 38,000 englilsh words (who knows how many pictograms - the written form of his day) about the Exodus.
Moses never mentions that, "Oh, by the way, God dictated to me (32,800 words) how the universe was formed, how man came to be, the origin of foreign languages, the origin of sin, how the world was flooded etc."
So, then just when did this dictation and transcription take place? Remember, Moses is in the desert with no stone to be chiseled on or clay to be inscribed upon.