I'm hoping to hear something this weekend.
There isn't much precedent really.
The first one was Leap Day in 2012, announced New Years Eve
The next 3 have been near Memorial Day, to kick off summer
Now, there is no way to know if they moved them to Memorial Day because they want to do them in summer or if they moved them because there was no Leap Day those years.
I booked a trip for Leap Day just in case. We loved the 24 hour day last year, even though we didn't stay all 24 hours. But it was awesome to have all of Adventure Land and Frontier Land complete by 8:00 AM