Noun
English Wikipedia has an article on:time standardWikipedia
time standard (plural time standards)
An agreed method of measuring time; a specification or standard of either the rate at which time passes, or of points in time, or of both.
This Ephemeris Time standard was non-relativistic and did not fulfil growing needs for relativistic coordinate time scales. Source: Internet
When the Coordinated Universal Time standard was instituted in 1961, based on atomic clocks, it was felt necessary to maintain agreement with the GMT time of day, which, until then, had been the reference for broadcast time services. Source: Internet