3:33 AM

All living things have circadian clocks which our bodies program without the use of external sources. Waking up at 3:33 am is a timed occurrence that the body is familiar with. For example going to sleep at 9pm is part of the circadian clock because leading up to 9pm the body starts to unwind, relax and drowsiness occurs.

Reference:
www.nigms.nih.gov