I believe that YHWH’s moedim (appointed times) began with time itself. Perhaps the specific dates were unknown to the people of ancient times, but YHWH always knew them and has more than possibly worked in sync with these special times. Jewish tradition states, for example, that Adam and Eve were created on [what we know as] Yom Teruah. Personally, I wonder if their banishment from the garden occurred on Yom Kippur?

Later on in Genesis, we see some dramatic events in the life of Lot that correlate with the appointed time of Passover. Whether you believe the events took place on the actual moed of Passover or not, I think there’s some lessons to be gleaned from the links we find.