Question: When does the physical birthday actually begin and end? How many hours of the day does it cover?Sri Chinmoy: Actually a birthday covers all the twenty-four hours. Suppose you were born at three o'clock in the afternoon. You do not have to take the twenty-four hours from that hour. Right after midnight you can begin to observe your birthday. When the calendar falls, after twelve o'clock, that is your birthday.
Sri Chinmoy, The soul's special promise, part 2, Agni Press, 1999