They will admit people from the fastpass line as a pre-show begins and fill in with people waiting in the standby line. With 2 shows running it seemed that they admitted a group to the pre-show about every 10-15 minutes. So if you arrive in the fastpass line just as the doors close you might wait 15 minutes. We were in the standby queue on a hot humid morning and I found the queue to seem to be VERY slow moving. It really wasn't bad, but it felt like it.