Hi, Kyler! We usually skip the day at the theme park on this day and spend our morning and afternoon at the pool, at Downtown Disney, and having a nap before the party. Being able to go in at four and party until midnight gives us plenty of time for the rides, and you will find most of them are open. While it is subject to change, if you do a search at
www.allears.net on Mickey's Not So Scary Halloween Party, you'll see a list of the rides that were open last year. The rides do operate through the end of the party, so you really can get eight hours in doing rides and things.
Because the lines for rides tend to be shorter than on a normal business day at the theme parks, we have always found that we can do more rides than we might get to in a typical day, plus we get to do the trick or treating!
We really enjoy the party, and the kids never feel like they've missed out on anything by not going the whole day. By going in at 4 o'clock, you can quickly visit the few things that won't be open during the party, so no one is sad if their favorite ride is closed during the party. Not that anyone notices when the party is in full swing!
Have a great time!