When an astrologer erects your natal chart she or he uses three pieces of information to do so, the date, time and the location of your birth.Most people know the day and location where they were born. There are rare cases of people who for whatever reason do not know for certain the day they were born. The more common situation however is an astrologer encounters a client who does not know for certain what time they were born. Requiring verification of the birth time from the birth certificate is the usual way to confirm what “Mother told me.” Responsible astrologers understand and communicate to the client that without the time of birth chart calculations are unable to determine what degree and astrological sign was on the horizon for that moment in time. That piece of information is reflected on the first house cusp or Ascendant. The Ascendant anchors the chart and determines the sign and degrees for the other cusps (divisions of the houses). It has major significance in chart interpretation. A thorough reading can not be done without it.
Suggestions for locating your time of birth

Contact the hospital where you were born and ask for their records department. Depending on when you were born the hospital may have put your certificate on microfilm. Ask for a copy of your original birth certificate and emphasize the importance of the document reflecting your time of birth. You may need to pay a fee for this service. Keep in mind it is not uncommon for this to take several weeks to a few months to receive.

It is common that after a period of time hospitals send their records to the bureau of vital statistics for the county, city or town where the hospital is located. If that is the case then you will need to direct your request with that department. Again anticipate paying a fee and a wait to receive a copy of your certificate with the time.

The following links may aid you in your search.

National Center For Health Statistics

VitalChek: Express certificate service

Family Birth Records

Using Dogpile, Google or other search engines may help further.