According to Vedic astronomy, the day is divided into 30 periods called muhurtas. Since the Vedic day begins with the sunrise and time of sunrise varies according to location and seasons, so do the times of the muhurtas in a day.
srimad-guror astakam etad uccair
brahme muhurte pathati prayatnat
yastena vrndavana natha saksat
That person who very attentively recites this astakam to Sri Gurudeva during brahma muhurta is sure to achieve direct service to the lotus feet of Lord Sri Krishna, the very life and soul of Vrindavana, at the end of his life. – Sri Gurvastakam
brahme muhurte cotthaya gopyah sarva grhe grhe
dehaly-anganam alipya dipams tatra nirupya ca
In each home the gopis rose at brahma-muhurta, anointed the doorways and courtyards, arranged the lamps, . . . – Garga-samhita 5.15.2
brahme muhurte cotthaya rama-krsneti ca bruvan
natva gurum bhuvam caiva tato bhumyam padam nyaset
One should rise at brahma-muhurta, chant the holy names of Lord Krsna and Lord Balarama, and bow down before one’s guru. Only then should one place his feet on the ground. – Garga-samhita 8.10.7
Brahma Muhurta roughly translates as “time of Universal Consciousness (Brahma)”. It is considered the most auspicious time for meditation, worship or any other spritual practice.
According to Ayurveda dinacharya or daily routine, rising before dawn is considered to be of primary importance for health and wellbeing; the auspiscious quality of the natural energy reflects positively on the consciousness of the individual. The sunrise increases Pitta – the quality of heat and light and thus aids digestion. Therefore it is important to wake up early and clean the bowels to avoid re-digestion of waste under the influence of the sun. It is for the same reason that the lunch is supposed to be eaten around noon everyday when the sun’s influence is at its peak.