Essentially this same thing happened during Boo Bash. I attended 2 of those events. During the 1 hour "transition" on one night, my family and I ate at Casey's until the party started. During the second party, we just got our wristbands (they had a wristband station by the old Stitch ride in Tomorrowland) and then went on a couple of rides that had short wait times. In our case, we did Small World and then Haunted Mansion. By 9pm the entryways to each "land" were manned by Cast Members lined up across the walkway policing for party wristbands. You'd just hold your arm up as you walked through. If you didn't have a wristband, they'd usher you to the front of the park.