It goes in bursts, and depends how interesting the thing I'm working on is. My sleep schedule shifts a lot, (I think I was meant for a 25 hour day) so right now I work from 7pm to like 5am.
The circadian cycle that regulates sleep (amongst other things) has a 25-ish hour period for most people, in the absence of natural time signaling stimuli (i.e. sunlight and noise). In natural conditions, sunlight in the morning readjusts your body clock in roughly +/-15m increments.
Recent research points to a faster way to adjust your body clock:
