Usually I go to bed around 22:00 - 23:30, when there is no work.
In my opinion, by sleeping 4 hours a day there is no problem, as long as you can manage your stress level properly and exercise diligently every day.
4 hours is way to short for me. Sleeping around 7 hours is optimal, if I sleep too short or too long I am going to feel it all day and won't be as productive. Recently I started to go bed 1 hour earlier and wake up earlier too so I can do important things in the morning.
Defend on your age mate, because when you get Older even if you wanted to sleep more yet you can't because your mind is awake and you may not get sleep from that 4 hrs time after.