GPS sends time in its data stream so doesnt need external clock, most car clocks use this now I believe though my nissan leaf is exactly 4 hours out to the microsecond so some programmers ignore timezones :-)
But that is relative to the GPS epoch. I have a handheld Garmin that needed a firmware update after the last GPS week rollover because it didn't deal with the epoch change and displayed a date 20 years in the past. Anything built before 2019 could be prone to this.
I am pretty sure they forgot to account for the probably 9600 baud serial rate the GPS transmits the exact time so it is sure in the milliseconds range if not half a second
