I went on September 11 last year, and usually visit that week most years. Regarding the hours, the hours for all parks are pretty much the same each day during that time. Generally, Epcot, HS, and AK open and close at the same time, even on weekends. Of course, MK will close early on party nights. This should not be a factor when choosing which park days. My only suggestion is to plan around party days for MK, and to avoid Epcot on weekends due to the Food and Wine festival. These will be your obstacles when planning your week.
Do you do MK on the day of the party? The party will use a lot of energy. You are paying big money to be there. To see the characters, to see the parade and fireworks, to do the treat trails, and to get on rides with minimal waits. It's a go-go-go night. You need your energy. I highly suggest not going to any park that day. This is our strategy. We need our energy for the night. We loop the park at least twice during an event. September is hotter than heck. What you don't want is to burn your energy the 8 hours prior to the event and not have energy for the 5 hours when you actually need the most energy. You can also get in at 4pm with a party ticket. So, if you burn one of your MK tickets, it will only be for 8am - 4pm. You can use that ticket for a full park day, from 9am-10pm. You will also get a separate fireworks show as well. Or you can have a relaxing day, doing the things you didn't do during the party, or use the party to do things you didn't do on your full park day. Of course, it will be busier on non-party days. This is true. However, if you only have 4 days to actually do parks, you will have to make a tough decision (which park to cut short) and have a very very long day followed an early morning, presumably, for the next park. Just know that 4 straight park days with a party thrown in is exhausting.
Park reservations? The week you are going is the slowest week of the year. No need to make park reservations now. The party dates will be posted in the next couple of months (announced on April 28 last year) and you will have plenty of time to plan your week and make your reservations after the dates are announced. Of course, you can make your reservations if you want to and then change them. FYI, here is the official thread from last year that had last year's dates to give you an idea of what days the parties fell on:
https://www.disboards.com/threads/o...-scary-halloween-party-lets-boo-this.3882475/.
