Comment GPS does output UTS as soon as it has a lock. (Score 1) 290
You confuse "GPS time" with GPS as a source for precision time. The difference between GPS time and UTC is broadcast every 12 minutes in the data stream, and includes the accumulated whole second difference, as well as drift value to correct for sub-microsecond. GPS receivers have access to this information and generally output UTC as soon as they read the offset value. Since the offset does not change often, it can be stored and used on subsequent startups, though this is a vendor specific decision. Though I've heard that they exist, every receiver and time source I've used outputs UTC by default by the time it downloads the full almanac and starts reporting position.