Contrary to popular belief, there has been no study supporting the 11pm-2am critical sleeping time rule. i don't how or why people came up with it... haha. strange sia.
The key to good and fruitful sleep lies in sleeping enough and according to ur inner circadian pattern. all of us have a circadian pattern.. which explains why all of us feel sleepy at different times during the day, as well as feel sleepy at different times in the night. We should actually go to sleep when our drowsiness takes a deep dip... 'cos that's the body signifying to us that it's the natural time to sleep. For myself, this deep dip comes at 1.30-2am.
If you find yourself tossing and turning on bed, with thoughts racing through your mind, you're recommended to sleep 3-6 hours later because YOU ARE SLEEPING TOO EARLY.
if however, you find yourself sleeping for a sufficient number of hours, yet still feel tired throughout the day, you should try going to sleep 3-6 hours earlier. the key to this is once again, know your own body. find the optimum time to sleep and you'll produce greater fruit in the day.
and please sleep at least 4 hrs or so.. you NEED the REM sleep.
for cited studies, go search yourself. i'm lazy to state it here.