It's hard to say, because there are so many variables: how many CM's staffing the desk, how many people in line in front of you, etc. There may be a small line, not because people will be checking in at that hour, but people may be checking out. The lines could be longer if, for example, they have a big convention or other group in house that's checking out. Once you get to the desk, provided it's a straight forward check in, it usually takes about 10 minutes start to finish. It shouldn't be that busy at that time, but it could be. If you are trying to get somewhere else by a certain time (dining ressie, rope drop, etc.,) I would allow at least 30 minutes and hope for 15.