If we timeline Michael wooing Kay in New Hampshire as '47 it leaves no time for Sicily during which there were Gangland war, Apollonia, Sonny is killed, getting Michael back and more

If he "settles all family business" in 1955 working back and rounding off to 'six' years, Michael's return to the US is perhaps '49 still --too many years for the Corleones to be pretending that they were "weak" and ready to be knocked over. let alone eight

1. Michael's been back longer than a year
2. New Hampshire 1951?
3. Anthony born 1952?
4. He was 3 years old in the Garden scene presumably 1955 Vito's death and the assassinations