You are right. But think about this. A few high school kids in an empty Hall Of Presidents theater for 30 minutes. It's not the smartest thing to do. It makes sense not to have the Jungle Cruise open, since it's a spieling ride (and kids don't listen), and after what happened on the Ferry and Splash on Friday, they should have no water rides open.
I had never epxerienced Grad Nite as a guest, but even working it, it was tons of fun. When the Blast Off party started, kids went running right to Space Mountain. The standby sign said 45 minutes, since it wasn't changed from when the park closed to day guests, so many kids stopped running and ran the other way. Bottom line: alot of running lol.
Oh, and the dancing...what did my virgin eyes do to deserve that.
You'll have an amazing time for sure.