Seems pretty conclusively tied to the big reveal/reward for the event, see Aequorin's posts in this thread:
https://www1.flightrising.com/forums/frd/3021228/1
So whatever's going to happen is significant enough to necessitate downtime. (And as mentioned elsewhere here, the impatience I'm seeing is making me feel rather jaded and old. Yeah, it'll be fun to find out what's what, but the 'We have to wait one extra day??? Nooooo!' mood just can't resonate.)