I work graveyard shift and usually have to be asleep by 6pm, so I'll go with 8pm being late because of conditioning =P Even if I manage to sleep in til 8am on my days off, when 4 and 5pm roll around I get sleepy automatically.
I'm nocturnal (and an insomniac) by nature, but unfortunately life just doesn't seem too willing to let me live by that schedual
That said, for me, "late" basically depends on what's going on tomorrow, if I have to be up by 6 am, then midnight's starting to push it. If I know I'm going to be able to sleep in, though... well it's entirely possible I'll still be up when the sun rises.
I consider 3 a.m. late at night. It is oftentimes the darkest time of night. I am usually awake at that time-reading hubs & answering questions. If I am feeling sleepy, I just put a horror movie on my portable dvd & just go to sleep.
I don't just mean hubpages, though that counts, too. I mean when you feel that creative urge and you want to sit down and let the language flow until something beautiful comes out, whether it's a short story, a...