Can the Real Time Clock (RTC) on receivers be used elsewhere?

In general, this is not advisable. The RTC was only intended to keep APPROXIMATE time in order to decrease search time when the receiver is restarted, it was not designed to be used as an accurate time source unless satellites are being tracked. When the receiver is actively tracking satellites, the time being reported by the receiver is extremely accurate as the RTC is slaved to GPS system time. However, if the receiver suffers a loss of lock due to satellite blockage or other system problems, the RTC will enter a free-running mode. The RTC will continue to run, but errors of up to several seconds a day may develop, depending on component tolerances.