system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] How does the Federation base time? Surely not all planets have a 24 hour rotation.
gpt
They tend to use local time for planet-based assignments.  Unless a planet has a radically different schedule, like night lasting a month, people adapt.  Most planets seem to have like a 20-30 hour day.  

Ships tend to use 24 hour days.  This seems to be just military convenience, as it allows for 6 hour shifts or 8 hour shifts, depending on captain or crew's preference.  Enterprise-D used three 8-hour shifts, occasionally using four 6-hour shifts that the crew disliked.  Deep Space-9 used the four 6-hour shifts and seemed to prefer them.