Not having a fixed schedule doesn't particularly bother me, but being disconnected from the day when I go to sleep after the sun has been up for a while is a bit bothersome. When it gets to that point I usually stay up all day so I go to sleep at a "normal" time.
Waking early has some benefits: working for a few hours before your coworkers are awake is a nice feeling, and I get home in time to run and and cook dinner at a reasonable hour. On the other hand, if a crisis happens at work, everyone else's 9 hour day is my 12 hour day
And having a girlfriend doesn't make it any easier.
I stay up late out of necessity. I work from home (on my startup) and I have a large family. That means the only time I get uninterrupted time is after 11:00pm. I need the uninterrupted time for the difficult problems. Other work I can bang out during the day.
The down side is I sleep until noon.
When I had a 9-5, I stayed up until 2:00-3:00 got up at 8:00 and was in the office by 9:00. I would catch up on sleep over the weekends.
But I have a 9-5 job and like to get into the office early when it is quiet as you can get more done that way.
So I try to get to bed before midnight - of course my pet projects suck me in and I lose track of time some days!
When I'm at school, however, it's usually 2:00-3:59 or after 4:00.
When I'm at home with my family, it's before 10:00.
My most productive times at work seem to be mid-late mornings. My most productive time for hacking seems to be 10 pm - 12 am, which is unfortunate because I end up neglecting one of sleeping and hacking.
12-2AM: Life is busy and I've lost track of time but I am always in bed by 2AM.
10PM (ish): My body is in tune with the sun and so I'm waking up at 5-6AM by the light. I find I usually need naps to make it through the day but this schedule is usually my most productive. I get onto this schedule when I crash early from staying up late for an entire week or when I spend time outdoors (e.g. camping for a week in Yosemite under the stars).
I regularly start at 10am+, sometimes 11 or 11:30. That doesn't keep me from leaving at ~6pm - it's mostly to have some office time (highly overrated in my opinion).
I'm not going to bed before 1pm, most of the time I pass 2pm as well.
Of course with uni I try my best to change this and make as much stuff as possible, ideally night classes would suit me but no chance of getting them.
So yes, late night is the way to go for me. While other sleep, I dream.
I sleep 5 hours when I'm not working out and around 8 hours when I am; which means my sleeping hours are either [12 AM, 5 AM] or [10 AM, 6 AM].
Should i vote "before 10:00pm" or "after 4:00am"? :-)
In the winter, 3 o'clock. No need to rise early when it's dark and storming outside.
I wish I could do the summer schedule all year.