Not sure if school time takes away from overall time. This should be made clear in the documentation. My issue - my kids have their devices at school where they have to use them in class. If I set an overall time of only 1.5 hours without setting school time then they run out of time either at school or after they come home.
I would think that if you set school time it should allow them to use during the school hours and then leave them the 1.5 hours outside the school hours.
Does anyone know the answer?