Comment by layer8

UTC-style time should never be used as unique identifiers by itself, and computer clocks telling such time should generally not be assumed to always have monotonically increasing output. Most systems are sufficiently sane that they don’t critically rely on such assumptions.

The most interesting issue regarding Mars is that time elapses slightly faster on Mars than on Earth due to relativistic time dilation (according to https://space.stackexchange.com/a/33592, by 0.17 seconds per year). Conversion between Mars and Earth calendars will eventually have to take that into account, possibly with some kind of leap second mechanism.

Overall, I don’t think it will be too much different than what we already do on earth with regard to different calendars and timezones. The one novel aspect will be the difference in length of day.

Regarding a common solar system time, there is BCT and BDT [0][1]. Astronomers already have to deal with that. Another interesting webpage about time scales is [2][3].

[0] https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time

[1] https://en.wikipedia.org/wiki/Barycentric_Dynamical_Time

[2] https://www.ucolick.org/~sla/leapsecs/timescales.html

[3] https://www.ucolick.org/~sla/leapsecs/deltat.html