Ayurved says a healthy person should wake up at BRAHMA-MUHURTA. i.e.- Atleast 96 minutes before sunrise (i.e.- NAADIKA-DWAY).

It is  Vaata dosha dominant time which helps in  bowel evacuation fluently without any liquid intake which is said to be the best indication of AGNI (digestion process).

The time of VAATA dosha is from 2am to 6am

One use to make sure that bowels should be excreted by 6am, so it is must to perform slight exercises and         

Getting up by 4 am ceases ageing process & increases praana level of body which gives a glowing appearance.