IF they continue with past year's experiences, you can enter the park at 4 pm with your party ticket AND you can do FP+ for those hours before the party begins. The last FP+ has to be completed by 6:30, so you do 3:30-4:30, 4:30-5:30 and 5:30-6:30.
We did a Sunday party last year and only focused on the rides and had a blast. The only wait we had was 7DMT, and even that was only about 20 min. We rode it a second time just after the fireworks, and pretty much just walked through the queue and onto the ride.