GPS satellites contain atomic clocks, so the timing of the GPS signal is very accurate. When a GPS receiver has locked on to the GPS RF signals, which transmit continuously at 1575 MHz, then its own internal clock routines become synchronised.
This synchronisation allows the internal clock routines to produce time to an accuracy of 10 ns.
The update rate of the GPS receiver is a limitation on how often it can sample data from the continuous RF signal. Most people first experience GPS using low cost simple GPS receivers that are only able to sample at 1 Hz. However higher priced, higher specification GPS receivers are able to sample at higher rates.
Racelogic GPS receivers are at the moment able to sample at 100 Hz but it would theoretically be possible to sample at 1000 Hz.
Regarding time, in the case of GPS receivers in a Racelogic VBOX 3i, we pass on time to our users at a resolution of 0.01 sec and update rate of 100 Hz.