Mine hides under his plants to sleep.
He doesn't seem to have much of a schedule, but I like to think that he's like a cat. You know, sleeping for a little while, then swimming around and exploring for a little while and back to sleeping (or maybe just lounging). Of course, since I personify every pet I've ever had, I also like to think that he goes to sleep when I do (i.e., when I turn out the lights), but I'll never know, since I'm sleeping. I do know that he gets really excited when the lights come back on in the morning.