So imagine we get to Mars, establish a colony.

Mars has a day which is 24h 36m.

We could have all of our Martian colonists adhere to an Earth day of 24 hours, with sunrise and sunset drifting around the clock, or we could have them observe an extra 25th hour of the day that lasts 36 minutes.

Or, we could define the Martian day as 24 Martian hours of 60 Martian minutes of 61.5 seconds, with seconds the invariant interchange time between planets.

In turn, seconds stop being a unit of human timekeeping, and everyone just uses decimal minutes as the final subdivision.