According to Biomedical clock, some called it as Circadian Cycle, in Ayurveda it called as Deenacharya, human body organ start to take rest 2:30 hrs after sunset, and if one sleeps at that time and wake up early morning 2:30 hrs before sunrise, then all his hormones get settled during sleeping hours and internal organs refreshes at the time of getting up.
So early to bed and wake up early morning keeps your body organ to work at its optimum level, consequently avoid diseased state. Thank you.