Who wants clock noon to be the midpoint of the workday? The canonical working hours are 9am to 5pm [Parton 1980] whose midpoint is at 1pm. Many people work earlier and/or later, but my impression is that it's pretty unusual to have the midpoint at noon.

(Schools tend to have earlier times. It's not so unusual for a school's workday to have its midpoint at about noon, I think.)