As I type this it is 2am. I am not tired. I will likely end up going to bed at 5am so as not to arouse suspicion that I have been awake this late, though the time between now and then will be filled with various activities now that my forum run is basically done. In the last 48 hours, I have had 3 hours of sleep. I'm just going to take a guess and say I'm nocturnal.
As for how long, Not always, there were times when I was very young that I went to sleep early (Lasted till the age of somewhere between 7 and 12) but in my recent life I have found that I stay up at night, and will usually sleep late during the day unless something important is going on. Probably comes from the fact that I don't really need a lot of sleep to function (I could survive another week at the very least with 3 hours of sleep to 48 hours of being awake easily), and don't get tired easily. Trying to sleep whilst I am not tired is pointless, and as such I stay up and do stuff. Sometimes when I have nothing to do, and am really bored, I will just go to sleep at a normal time, but I'll still wake up late as that is more of a 'Bed is warm and I CBF moving' sort of thing than a 'I'm tired' sort of thing.