Bingo. If I'm doing the night-time coding thing (or photoshop designing or anything else) I could start around 10pm and easily still be there at 10am, even without the use of stimulants (caffeine or what have you).. you just hit that zone in the peace and quiet; the work streams out and the time floats by.

During the day, with people around, phone calls going on, the Irish web scene (forums/IM/blogs/etc.) all a-buzz, I'd be lucky to last an hour or two without getting distracted for "15 minutes" and totally kicked out of any concentration zone I might have been in.

Although maintaining 'normal' hours does have it's advantages too. It's difficult to get and maintain work when you're only awake by night.