When I was last working on sci-fi writing (for a game I was running), I came to the conclusion that most places that are in contact with galactic society (in a setting with FTL travel and communication) would probably have one calendar that is standardized for official use, and at least one that is local to the planet. Systems with multiple inhabited worlds might have a system-wide calendar in addition to the individual calendars.

On the other hand, people living on ships, space stations, or remote outposts might track everything in standard time.

Dealing with characters who negotiate contracts across interstellar distances and frequently move between ships and planets made keeping track of things like "what time is it planetside if we rest for 8 standard hours on the ship?" and "if we agree that this contract in another system begins in 30 standard days, but we're occupied here for another local week, how much time do we have for travel?" enough of an annoyance that I went looking for a program that could automatically track these things, but I don't remember if I ever found one.