As
@Rob562 indicated, if you enter at 4pm, your ticket will be scanned as the party ticket. Therefore, since you enter via the party ticket, the FPs are for your party ticket. It doesn't really matter when you make your selections -- you haven't entered the park yet. All the system needs to see is that you have valid media for entering the park that day. Now, if you enter and use all three FPs before 4pm (meaning you had to have used your main pass), you don't get another three between 4-7 pm. You're limited to one at a time after the first three until 7pm. Finally, if you have an AP, not per-day tickets, it really doesn't matter which media the FPs are applied to. You still only get three per park per day.