If it weren't for school I'd probably have a pretty messed up schedule (wake up late, sleep late) with all my work being done at night.
Though, because I hope to be an astronomer some day, perhaps that isn't such a bad thing
To tell you the truth I can be either. I generally feel most alert when I wake up at 9 am and go to bed at 11pm, but the times I have woken up around 5 I've been able to get things done too. I think the common denominator is that there is nobody around to distract me.
Graduate school (first stint): night owl, didn't start until 9 pm or so, finished up when my apartment mate was getting up for his 8 am med school classes. Second stint (PhD work, post marriage), 9-5, with the occasional get up at 2 am to work until ? (I'd really get a lot done during those early morning stints).
Real world (after graduate school): I'd get to work between 6:30 and 7 in the morning. Now that I am unemployed and looking for employment, my most productive time is still between 8 and 10 am.