You don't need to be at the exit at the posted closing time. Park closing means they close off the ride entrances at that time. If you're already in line, they keep running the ride until everyone in that line has ridden. Major shops often stay open until half an hour or so after closing time, and fireworks may start at closing time and run for 15-20 minutes. All that being said, please be considerate of cast members who want to get home and sleep and make your way to the park entrance promptly after fireworks or your last ride/purchase is finished.