timdux

Mars calendar, each year has 24 months: https://en.wikipedia.org/wiki/Darian_calendar

Solar system time: https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time

Yes, that's the clock holdover circuit, usually built using a OCXO or double OCXO or rubidium clock. It's good for 4 to 24 hours. Example:

[0] https://www.rakon.com/19-rak-product/rak-product-ocxo

All terrestrial base stations (1) require GPS signal for time synchronization. Most of them can run for 4 hours - 24 hours without GPS, but that's it, after that holdover period it's dead.

There is no GPS signal on the moon. That's a problem.

(1) except micro base stations