Back when I lived alone and worked as a full-time freelancer (thus mostly free to set my own hours), slept from about 4 a.m. to noon. I’d write from about 7 p.m. to 2 am.
Left to my own devices, i settle into a 28 hour day, with 20 hours awake, then 8 hours of sleep.
Highly annoying that the world saw fit to work on 24 hours
Some of my retired friends are still on their work schedule and are up every day at 5 or 6 a.m. and in bed by 9 p.m. It took me about a week to get to sleeping from 1 or 2 a.m. to 9:30 or even 10. Hell, if I’m supposed to be somewhere by noon, I have to set my alarm.
Ha, that sounds familiar. I’ve been retired a while now; I’m up till 10 or 10:30 PM and get up around 4 AM.
I’m between summer jobs and school right now, so I’m on my preferred sleeping schedule, which is 2-3 a.m. to 8:30-9:30 a.m., with a nap of about an hour and a half somewhere between noon and four.
For most of this summer, I was on a 10 PM - 6 AM schedule. I went to the UK in May and came back jetlagged, and after a few days of confusion, that’s what I settled into. I’m a morning person, but I never got enough sleep in college because I had stuff to do (and neighbors who stayed up late talking on the other side of the very thin wall). Getting enough sleep and waking up at six was great for me. Then last week I went on a trip that involved some late nights, and this week I’ve been sleeping from about 1-9 AM. I don’t like it because it feels like the day goes by too quickly, but I’m having trouble adjusting back the other way (the Olympics broadcast schedule isn’t helping). I’m hoping I’ll actually manage to get a job soon, and that should help.
So I think 10-6 is ideal for me, but it only worked because I don’t have a social life. 
(I’m 22, for the record - I wonder when I’ll sleep when I’m old!)
When left to my own devices, I’ll sleep from about 6 to 10 in the evening, and then from four to ten in the morning. It’s a very rare thing that I can actually do this, but good God is it glorious when I can. Apparently, my circadian rhythms believe I’m a cat.
My mom was nocturnal, and I picked that up from her when I was younger. I could stay up all night and sleep 'til the afternoon.
Lately though, I’ve found my rhythm is to get up by 7AM, and hit the rack by 10 or 11 PM or so. I almost always wake up around 4, or 5 or 6, and as long as I know I’ve got a pot of coffee waiting, I could get up at any of those times without a struggle. I don’t use an alarm clock. I hate those things. If I have to wake up extra early for something, I will, because my subconscious worries I won’t.
I have a job where unless I have a meeting, I can show up whenever (though not every day.) From June 1 to August 1st I only go to the office if I have to (as do all my coworkers whose job doesn’t have the title “assistant”.) So I do get to play with my sleep cycle.
In the summer I’ll sleep from about midnight to 6:30 a.m. In the winter I’ll sleep from 11 p.m. to 9 a.m. My sleep cycles are very dependent on daylight - the more darkness, the more I sleep.
I pretty much have the sleep cycle I want - to bed at 2 AM, up at 7. Much more and I feel sluggish and head-achey all day.
Most of you would only sleep 8 hours? Jeez. I’d get at least 10. Probably from like 2am-noon.
I settle into a 35 hour day, with 25 hours up and 10 hours asleep. Born on the wrong damn planet.