Abba, that is an interesting suggestion you made about parents changing their non-mandated bussing children to a further away Yeshiva, this making him a mandated bussing student (and eliminating the savings for the board.) It is well worth considering.
Regarding my earlier suggestion that the yeshivas modify the times, the bus drivers cannot legally dump minor children on the street in front of a closed, unsupervised, school. So the driver will be forced to wait till the Yeshiva opens up. Meanwhile the next shift of students from the other schools will need to be picked up while the first bus is waiting.