School began at 7:50 am for us. So that time worked well for parents and 9-5 sort of times. It gave enough room for 8-4 or 8-5 parents and long commute parents. Or parents who want to drop off and come back home first. If you make the school start time 9 am as well, if a parent helps their kid get ready and/or has to be around until the kid leaves for the bus and/or has to drop them off, they wouldn’t be able to unless their commute is short.

I don’t think school times can be pushed much. Maybe 30 min max without seriously disrupting parent’s schedules if that’s a concern.