School

For primary/grade school, for practical purposes, whatever hours are least likely for working parents to require childcare during the week... probably 8:30am-3:30pm.

For older students (post-secondary and high school) it doesn't matter as much, but there's definitely benefits to doing a compressed week i.e. have a 4-day week instead of a 5-day week, but with more hours per day.
Benefits being:
Less commute time per week (which is also better for the environment)
3-day weekend
Easier to get a part-time job (fewer classes for a potential employer to have to schedule around)