Base 12.

Nah, base 12 number system with the same logic as metric. But it's probably too late to switch to a different number system.

It's useful. But when was the last time you used it? You usually don't say a twelves or a third or a sixth of an hour, you say 5, 20 or 10 minutes. Half and quarter are available the same in decimal time.

It's more a matter of habbit. You know what a second, a minute and an hour are because you had all your life to precisely learn it.