I agree that it seems a bit rushed, but spring break is probably dictating that as others have mentioned. As for the original Dumbo, it is likely getting a full refurbishment which is a lot easier to do backstage somewhere. And if reports are correct, we probably won't see either tent open this month.
I noticed that as well, it seems to be there to cover the side of the LM building that you will be able to see. Why they waited until now is anyone's guess. Maybe they needed to finalize the SW perimeter before finishing the rock work on that side?