Your chart
Why your birth time matters more than the planets
People are often surprised that two charts cast for the same day can look completely different. The planets are nearly the same. What differs is the lagna, the sign rising on the eastern horizon at the moment of birth.
The fast point
The Moon moves about half a degree an hour, the Sun about a twenty-fourth of that. The lagna, because it follows the Earth’s rotation, moves through all twelve signs in a day: roughly one sign every two hours.
The lagna fixes the houses. In the North-Indian chart it sits in the top diamond, and every other house follows from it. Move the lagna by one sign and every planet changes house. Jupiter in the tenth, the house of work, becomes Jupiter in the ninth, the house of teachers and long journeys. Same planet, different life.
What to do if you don’t know the time
Use the closest time you have. A birth certificate, a hospital record, or a parent’s memory of “just after breakfast” is better than noon by default.
If your time is uncertain, trust the parts of the chart that don’t depend on it: the signs the planets occupy, the Moon’s nakshatra on most days, and the dasha sequence, which follows from the Moon. Hold the houses more loosely.
Time zones are the other half
A time is only meaningful with its time zone, and time zones change. India used several before 1955, and many countries have moved their clocks or adopted daylight saving more than once. Cosmic OS looks up the rules that applied at your birthplace on your date of birth, so a 10:30 AM birth in Delhi in 1990 is read as 10:30 AM in Delhi in 1990.