Time Standards

Time

Both GPS time and UTC are derived from the atomic time TAI, a reference used to define the time unit in SI, kept by 400 atomic clocks in the world. Both have time unit in TAI seconds. GPS time and UTC wer equal on January 6th, 1980.

Read - https://aviation.stackexchange.com/questions/90839/what-are-satellite-time-gps-time-and-utc-time#:~:text=Defined%20as%20equal%20to%20UTC,18%20seconds%20ahead%20of%20UTC.