My sleeping hours became somewhat erratic when I switched from working full-time to part-time in 2001. Instead of going to sleep around 11:30 PM and waking up at 7 AM 5 days a week, I was able to go to sleep around 1-1:30 AM on the now more frequent nonwork days and 12:30 AM on the work days (because I did not have to be at work until an hour later than before).
When my ladyfriend moved to my area, she had to go to sleep early when I stayed at her place on some weeknights even though I did not have to go to work myself. This made my sleeping hours more erratic.
When I ERed, I lost most of the early morning wake-ups when I had to get up and go to work. The only early wake-ups (i.e. needing an alarm clock) I had were the few times I actually had to be somewhere in the morning such as the school Scrabble tourneys I ran. I have about 4 or 5 per year.
But what has made my sleeping more erratic the last few years has nothing to do with any of that. Unfortunately, I have to go to the bathroom in the middle of the night more often than before. Not every night, thankfully, but it is often annoying to have my sleep disturbed that way.
Without any of these disturbances, I get up around 8:30 AM, give or take.