Sacred Mesa says "At the beginning of your upkeep, sacrifice Sacred Mesa unless you sacrifice a Pegasus." It also has an activated ability:
1W: Put a 1/1 white Pegasus creature token with flying into play.
My question is.. so let's say you use 2W to cast it. Then on your next turn you have your untap phase and your upkeep phase. Can you create a 1/1 white Pegasus token between your untap and upkeep phases to prevent Sacred Mesa's self-sacrifice clause from triggering?