Depends. I'm a network admin/engineer and there are times where I have to do maintenance late at night/early morning, or I'm rudely awoken by that fscking two-way pager at 3am in the morning. Basically if I get at least 6 hours of sleep I'm okay. I prefer 7-9 though.
If I kept regular hours it would be something like go to sleep somewhere b/w 1am-2am, and get up b/w 8am-10am. But, alas, that ain't gonna happen.