If you have tix for MVMCP and are in the park already, they round up everyone at 6:00 and move them into Tomorrowland were almost all the attractions were up and running until 7:00. (Stop and get your MVMCP bracelet after 4:00 to save some time). You do not have to leave the park and re-enter. We chose to do PS at Plaza at 4:45 so we grab a bite to eat and still have time to get in some of the rides in Tomorrowland between 6- 7. You do not have to have PS to stay in the park--just MVMCP tix. Hope this helps.
Michele