as long as you have a current room key you will be able to get your wristband. you don't need to get your wristband b4 the park closes though. you can go do whatever for the day, and then anytime in that extra 3 hrs go and get it, and go in. we were leaving MK on emh night a half hour b4 it ended, and people were still getting off the bus to go in for the first time.
they just start passing them out 2hrs b4 it closes to help with getting it done, and avoid congestion.
make sure it is tight enough on you, as i had one that kept slipping off, and had to go back and get a new one.