Ground re-synchronization happens daily. "The clock and ephemeris corrections are uploaded generally about once per day (but some times more often if needed to

Ground re-synchronization happens daily. "The clock and ephemeris corrections are uploaded generally about once per day (but some times more often if needed to maintain precision). The rubidium clock’s natural drift is large and might be of the order of 10^-13 per day" (quote from an engineer that works on the system)