We just received finalized (for the most part) itinerary and they said that the park will not be closing early on Sunday May 5th for the cheer celebration, they will be holding it after the park closes at 10. With that said though, not all teams will be competing on Sunday, and Sunday is final rounds and you have to qualify. I would say that probably about half of the teams will not be competing, so i would expect Sunday to be pretty busy-especially as the day goes on and it gets closer to the cheer party. Friday most teams either practice or compete, and Saturday most teams are competing except the ones that competed on Friday. If I had to guess, I would say Friday and Saturday won't be horribly busy, but Sunday and possibly Monday will have a lot of cheerleaders in the park. Lots of teams are traveling Thursday, May 2nd to Monday, May 6 or Tuesday, May 7th. I feel like the main issue is going to be kids traveling in "packs" because the kids all want to go on rides with their friends and/or family. The packages offered to cheerleaders and their families included 2, 3, and 4 day park hoppers so i would imagine most people will be traveling to the parks probable Friday-Monday. But, the good news is that Magic Kingdom will not be closing early on Sunday!
Hope this helps plan a bit!