<a href="http:&#x2F;&#x2F;www.usno.navy.mil&#x2F;USNO&#x2F;time&#x2F;gps&#x2F;usno-gps-time-transfer" rel="nofollow">http:&#x2F;&#x2F;www.usno.navy.mil&#x2F;USNO&#x2F;time&#x2F;gps&#x2F;usno-gps-time-transfe...</a> says: &quot;The GPS epoch is 0000 UT (midnight) on January 6, 1980.&quot;<p>So no, gps time is not defined before 1980.