In my reckoning the Book of Enoch comprises texts originally written between 3200 and 2750 BC. The Masoretic has Methuselah born 687 years after Adam was created. My own estimate of Adam being created 5893 years ago has Methuselah born about 5200 years ago or around 3200 BC. This is when Enoch told Methuselah he started to write - just before Enoch was married and Methuselah was born (when Enoch was about 60). Enoch was among humans (king over everyone) another 300 years (walking with God - living God's way). Then he went and spent a while in heaven then returned for a year with books to pass on. This would be around 2900 BC. Then another 100 years passed and some of the contents of one the Book of Noah portions of the Book of Enoch took place around 2800 BC when Noah was born and Lamech feared he might be son of an angel but Enoch assured this was not so. Then more dreams of coming Flood and the final parts of the writings of the Book of Enoch are completed originally by Noah it seems in his early years around 2750 BC at the latest. This chronology would have the Flood 600 years after 2700 BC or 2100 BC. (Note: Convention or tradition seems to have the Flood being much earlier around 2500 BC.)
