I have a very strange work pattern. Because I work from home, I'm free to choose my own working hours and I end up staying up all night most of the time.
I get up around lunch time, have a meal, coffee, etc and then work for a bit. I meet a friend in my local pub for a soft drink most afternoons, and I always watch the news and have a meal around 7pm. Then I'll be in front of the computer till 6am.
When I get bored of staying up all night, I don't sleep one day and I go to bed early evening and get up early morning the next day. I keep the early evenings and early mornings pattern for 10 days or so, and then my sleep cycle naturally drifts towards night time again :innocent:
Basically, for about 10 days a month I get up very early and for 20 days I'm up till 6am...
To answer your question. It doesn't f*ck my body up, because I don't have to get up at certain time, my sleep cycle shifts on its own. If I had to force certain sleeping hours on my body, then it might have been a different story.