Leap year happens every fourth year, except on the century, where it happens every fourth century (there was no leap year in 1900, but there was one in 2000). This occurs because the earth doesn't revolve around in 24 hours. It actually takes 23 Hours, 56 minutes and 9.4 seconds, give or take. This is a result of the Sumerians(?) who developed the 24 hour system not being able to use the atomic clock to accurately gauge how long it really took, presumably because the battery was dead. At any rate, they had to guess. And like most men, when they guessed, they weren't quite right. However, to their credit, they came remarkably close - even with modern conveniences, my wife can't get to a 9 a.m. appointment before noon (j/k).
Anyway, what I want to know is, since a unit of time is arbitrarily assigned (a second doesn't have to last the amount of time a current second lasts), why can't we adjust the gauge of time so that 24 hours is a day, as opposed to a day plus a little bit?