Unlike the timing outputs, the 10 MHz frequency output is not affected by propagation delay.  Since both the basestation and the EndRun unit are stationary (they don't move in relation to each other) the frequency is extremely accurate, to parts in 10 to the 12th over 24-hour averaging times.  On rare occasions, a basestation might experience a GPS outage, as when the GPS antenna is damaged.  Under these conditions the basestation's GPS receiver would go into a holdover mode and its frequency could drift up to about a part in 10 to the 10th over 24 hours.  An outage is rare, and one lasting 24 hours would be very rare.

Note that the requirement to maintain basestation synchronization during long GPS outages requires that each basestation have at least one high performance GPS time receiver controlling either an ultra high stability quartz oscillator or a rubidium vapor atomic frequency standard. Since it is very difficult to meet this performance using quartz oscillators, most base stations have rubidium units and redundant GPS receiver/oscillator units are common.