When we were there last year, it worked like this...
The party was scheduled to start at 7. We arrived at the park gates about 5:15/5:30, and were let in. The CM at the entry turnstile put on our wristband and we each picked up our trick-or-treating bag.
We wandered around Main Street for a while - a nice opportunity to take some pictures in the dwindling light, and were eventually told we could go to Fantasyland. I believe *only* Fantasyland was open until 7.
By the time we got down there it was probably pretty close to 6. The rides were all operating, but only those with a wristband could get on.
By 7, the whole park was open again.
I suspect that if you go to the park much earlier than 5, you would have to use a regular park ticket to enter.
HTH, Jeff
