So does that mean we switch over to metric time too? Or how about a metric calender? Working 10 days with only one day off?
well the thing is that "time" measurements are based on actual physical phenomenon, while all the other measurements of volume, length and mass are just made up increments that used to be based on unreliable quantities of things and then eventually agreed upon as a standard use.
A day is defined as as the 360 degree rotation of the earth on it's axis. If you don't have any math system (or you believe in a geocentric universe), it's obvious to everyone that a day is the length of time between the sun's passing over the horizon.
With simple addition you can look up at the position of the sun, the moon and stars and count the time it takes them to return back to the same spot they they are in right now, which is 365 days- the time that it takes the earth to rotate around the sun- a year.
Each cycle of the moon is roughly 29.5 days, a month- with the days split up and adding on a leap day to make them all even.
Now it gets a little bit more complicated. why are there 7 days in a week? because if you divide the number of days in a month into quarters you wind up with 7. And what is the physical phenomenon that this increment is based on? None. people just made it up because they liked the idea.
So why are there 24 hours in a day? Because people incorrectly assumed that a day is equally divisible in half by daytime and nighttime (this only occurs twice a year. If you are in the northern hemisphere it will be happening in 2 days, on march 20th. Lucky you.), and they just happened to like the number 12.
As far as 60 minutes in an hour and 60 seconds in a minute, well I guess if you divide a day into quarters you get 6 hours, and if you divide 6 by 360 (the degrees of a rotating circle, which is believed to have been based on the number of days in a year) you come up with 60. No, it really doesn't make much sense either, but they stuck with it.
The point of all this is that if you tried to divide days and weeks and hours and minutes and seconds into increments of ten, it would really make things fucking complicated, and that is why even the metric system accepts these "time" measurments.
As Mongo pointed out they have since came up with precious numbers to calculate mass, volume, length, and time based on physical phenomenon (mostly derived from the speed of light in a vacuum, one of the few universal constants) This system is really the only one that makes sense to me, but these numbers are confusing to the average person.
the reason that they invented the metric system is because it's easier for people to understand than any of the other systems. if you have a number divisible by ten, what it really means to the mind is that you have a number divisible by one and then zeros, which are nothing. that is easy to work with.
if you were to multiply say, 10,000,000 (ten million) by four, you just have to add one by four and then the zeros. = 40,000,000 (forty million) easy. that's essentially one calculation point.
But if you had to multiply by a more precise, but more complex number- 9,978,316 (nine million, nine hundred and seventy eight thousand, three hundred and *******) by four- basically you'd be calculating seven times as many points in your head. Harder.