A former fetus should recognize that we would be better served starting our calendar (and making it a big religious event) with the Annunciation. This is when God came to be one of us. His birth, sacrifice and resurrection all follow from his Incarnation, which happened in the womb.
What would be better, would be to follow God's calendar. The important dates, among many others, are his birth and Crucifixion. These dates that are important because we were given them ahead of time in that we may know that God exists.
Not knowing the times, as is the case today, is itself prophecy fulfilled.
Maybe, but we don’t have a date for that, do we? Still, it wasn’t His incarnation or His birth that saved us from sin, although they were necessary parts of the plan. It was His death on the cross that paid the price. So, if I had the power to change the calendar (and I’m not Anti Christ, I won’t even try) I would start the calendar on the day of the crucifixion!