I have serious trouble with my circadian rhythm, I really prefer the night to develop any activity, It happened, usually, problems that I couldn't solve in maybe 2 or 3 hours during day times solving in less than half an hour at 3am, you tell my professors to have my test at that time...
Since I was a child I go to sleep late, there where no chance for me to sleep at 10pm, about 1am much likely, my sister was always sleep after 9pm, so is not because my home environment. Then, at highschool I started to work in a pub, even if it's normal to get eventual times at there not working, working fri and sat up to 8am and probably wed up to 5am (school mon-fri 7am) and sometimes wed to about 5am also. It wasn't a problem for me, just strange for some people, I really sleep monday nights, I expend one month only sleeping mondays many hours and about 2 hours the rest of the week, I was at my last year and between school, parties and work I just hadn't time to sleep other than monday. I don't know what doctors would tell about that... I usually don't have trouble to change my hours, I doubt I would have jet lag, never went to the other side of the rock tough. Eventually I get a couple of days to sleep, this weekend I had one of those and was nice, but then I just can't stand waking up in the morning unless I really have to, and even then is hard to sleep before 3 or 4 am, sometimes even later.
It would be neat to have longer days, but you have to tell the earth to spin slower... I had been in a longer day myself, maybe 26 or 28 cycle, it's nice but it's hard to stand, because of two things, one is commercial hours, which makes hard to go out and buy things when you need them. The second is the people around you, everybody thinks calling at 11am or 12pm is a good time, if I am awake at that hour is because I'm busy! If I sleep 4 hours in a day, my dad WILL call me just at the middle, no matter if it's morning, afternoon or night. It's not really easy for me the timing, and sure for many other people, but it's true that a little more flexibility would be neat, as physicist says, nature is wrong...
JS