Lol, I thought the same thing in my first RP. It was some Adventure one and I waited for 12 hours after my character went to sleep to post again. Looking back, I feel pretty stupid. :P
Well, you gotta think they are asleep and that it's no fun to be RP about being asleep.
It's kind of like you being awake and asleep, it doesn't feel like the same amount of time.