I don't think there's any canonical mention of it, but here's how I see it: Years, hours, minutes, seconds, the old standards from Earth are used. Days vary a bit, but almost always something close to an Earth day, and the local "daylight" settings and work schedules will match the day length used. On Mars they use Mars days (37 minutes longer than an Earth day), as do most habs in orbit around Mars. As far as I know, there are no other places where local conditions warrant a local day - Mercury, Venus and Luna have too long days, further out sunlight is too faint it, and mostly people are not living on the surface of something where the direction to the sun matters anyway, so the majority will have to pick something. Where they have free choice, some places have stuck to Earth days, others use Mars days (encouraged by the Planetary Consortium this is spreading). A few places use some multiple or integer fraction of a local system feature, or maybe a pet theory about optimal sleep cycles, but mostly it is Earth or Mars days.

Most habitats have a revolution so slow (if at all, if the concept even applies), that the idea of hosting a local version of a 'day' (and thusly, hours, minutes and seconds) have no useful meaning. The only real exception would be Mars. Combine that with the fact that everyone does come from the common cultural basis of Earth, it's pretty much expected that everyone standardizes on Earth as GMT. If your local habitat has a different day-length, your muse will happily swap back and forth between local time and Earth-standard as appropriate, without lag. As a GM, feel free to stick to Earth time unless it's convenient to do otherwise.