I truly hope this follows and helps. It's far more profitable to count time from creation or AM (Anno Mundi) Hebrew: The Year of Creation.
(Refer to Genesis 5)
-Adam Born 0-1 AM
-Seth Born 130 AM
-Enos Born 235 AM
-Cainan Born 325 AM
-Mahalaleel Born 395 AM
-Jared Born 460 AM
-Enoch Born 622 AM
-Methuselah Born 687 AM
-Lamech Born 874 AM
-Adam dies 930 AM
-God takes Enoch 987 AM
-Seth Dies 1042 AM
-Noah Born 1056 AM
-120 Year Warning 1536 AM (Gen. 6:3)
-Shem Born 1558 AM
-Methuselah dies 1656 AM
-Flood 1656 AM (Noah is 600 Gen. 7:11)
-Arphaxad Born 1658 AM (Gen. 11:10)
With a proper timeline in mind, here's what we have;
Gen. 5:32 "And Noah was five hundred years old: and Noah begat Shem, Ham, and Japheth.". Gen. 6:3 "And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.". Gen. 6:8 "But Noah found grace in the eyes of the LORD."
Gen 6:9-10 "These are the generations of Noah: Noah was a just man and perfect in his generations, and Noah walked with God. And Noah begat three sons, Shem, Ham, and Japheth.".
So we have Noah walking with God for 480 years from 1056 AM - 1536 AM. Gen. 6:1-2 narrative. Then 1536 AM God tells Noah Gen. 6:3 and then Gen. 6:4-6 are narrative, then God tells Noah Gen. 6:7 and Gen 6:8 is narrative.
Then we get Gen. 6:9 generations of Noah.
I hope this is beneficial. God bless.