While the park was good prior to letting in party guests at 4, it was a mad house, IMO, by 5 or 6pm with both crowds in the park. I’d have a plan for what you were going to do in that time, assuming that’s what happens this fall. One year, I did my shopping right around 6, and I had managed to get a dining reservation at 6:30. By the time I was done with my meal it was after 7 and they had changed to the Halloween music on Main Street. I wasn’t escorted out that year, but I suspect I would have been if I wasn’t naturally headed down Main Street to leave on my own.
Another year, I had naively thought I could make it to Under the Sea, People Mover, and Laugh Floor in the last 2 hours. The standby line for Under the Sea really took an hour, the People Mover line was winding well beyond its queue, and the pathway in Tomorrowland to the hub packed with folks. I gave up early.