My Three Garmins That Display World Time A Few Seconds Apart.

All GPS units are receiving exactly the same time from the satellites and GPSs are synchronised to this time internally (they wouldn't be able to get a 'fix' if they weren't), so the difference can only be in processing of the time and getting it to the display, I would be inclined to say that as there is a delay between real time and display time that the 'fastest' time is the most accurate, however the GPSs have their own internal clock and only use the GPS signals to sync. this clock, so it is possible for a unit to display the time too early as well as too late

I would try comparing the 'times' with a radio time signal (WWVB in the U S) or radio controlled clock, although I have several MSF / DCF77 clocks in the UK and they sometimes differ in displayed time, the differences in the times will always be the same as they won't 'drift'