Time is not a count. Time is a linear displacement, just like distance. As such, it only makes sense to start with 0. Did you ever see a ruler that starts with "1" at the very end? Of course not. It starts with "0", but they just don't bother to print the "0".

One inch is a displacement of "1" from the beginning. One hour is a displacement of "1" from the beginning. It's pretty stupid to arbitrarily call the beginning "12".