There is nothing irrational or impractical with ten hour days and ten day weeks. In fact it is in line with the metric system of measurements, which is the most rational and practical system. Time is the only important area where metric system of measurement was not introduced.
You make a rather big assumption here, namely that the metric system is 'the most rational and practical system". Based on what? The fact that we have ten fingers, making it suited to our needs? Hate to break it to you, but a year has twelve lunar cycles. That's our basis for time measurement, and has been throughout human history. Maybe it has something to do with the fact that nearly every living thing on this planet is biologically aligned to that cycle? Replacing natural months with unnatural decimal cycles seems like a very dumb plan to me.
That means metric years, months and weeks are right out, really. While a metric clock might still work, even though a metric calendar is useless, it still offers no benefits at all. It isn't more "rational," either. You have two perfectly valid frames of reference. One is decimal, based on our ten fingers, which is thus perfectly rational for counting things, and a good basis for weights and measures... and one based on the lunar cycle, which is perfect (and perfectly rational) for time measurement.
Does it make sense to start measuring shorter instances of time (days, hours, minutes & seconds) according to the decimal standard, when it is inherently illogical to measure longer instances of time (weeks, months, years) according to that standard? No, it does not.
Therefore, I firmly stand by the opinion, put forth by Anaxagoras, that decimal time measurement is an ill-conceived notion. One should also observe that when the French actually tried it, it wasn't actually well-received, and they abandoned it when the revolutionary fever finally broke.
Make no mistake: I'm a big fan of the metric system for weights and measures. Very sensible. Should really be adopted world-wide. But metric time measurement just remains irrational and unwieldy.
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