And the "second" is an SI unit
I never said it wasn't, and I never mentioned SI units, you brought that up.
The point about time is that a day, a measurement based on the Earth's rate of rotation, has been split into 24 parts, a nice number divisble by 2, 3, 4, 6, and 12, each hour has been split into a similarly nice number of parts called minutes which in turn is split into seconds.
A metric version of time would presumably have 10 or 100 hours per day, 10 or 100 minutes per hour and so on. 10 is not a good number for dividing and has been chosen because of the number of digits this branch of the Great Apes have on their hands.