Why do you need the exact time and hour of birth?
Well, at the exact moment you’re born, the earth would have been in a particular place in space as it orbits the sun. But also as the earth spins on its axis, it would have been in a specific location in its 24 hours cycle.
The exact time of birth is significant because the chart changed fractionally every 4 minutes.
This is why it is essential to try and be as exact as possible.
There is more information on Astrology42.com
about the birth chart and birth information.
If you do not know your exact time, you can check your birth certificate, ask your parents or check hospital records.