My alarm goes off at 6am but I am usually awake from say 5am - when it is light, the alarm is just for reference really, not to wake me. My breakfast porridge cooks on a timer to be ready at 6am which encourages me to get up but it will keep warm so I don't rush, I take an hour for breakfast.
I don't sleep through, I usually go to the toilet about 3:30am, sometimes 1am.
Is that enough detail :)
I used to work until 4am and sleep half the day but I chose to shift to this circadian rhythm based pattern and not a stressful rush and I feel much better for it.
I really can't cope on less than 8 hours of sleep for extended lengths of time. It completely wears me down and I get tired and ill. Usually what happens is that when I get up at say 6:30am I am completely exhausted by 7:30pm. If I get up a bit later I can usually function until at least 10:00pm.
I did the exact same thing as you, I would always go to bed at 11.30 PM every day and wake up at 6AM. After a while I'd wake up a minute or two before the alarm went off.
I drink coffee all day long to compensate.