I don't know TB. Mike tells Tom that they needed another 4 months to get all of the political connections tied in (How could they put that in temporal terms?).

I always thought that Mike's stepping into Vito's shoes was not what Vito had anticipated. Instead, he wanted Mike to become that Senator or Governor in order to help the Corleones. However, Vito's getting shot, the war, and Michael's having to take over the family ruined that timetable and objective.

Oh, by the way, the massacre was in '50.