access:conditional=permissive @ Mo-Fr 00:00-08:15,15:35-24:00; Sa-Su sounds like it'll work much better than what I suggested before. Potentially throwing on Public Holidays (PH for syntax) would be good too.

Can't recall the last time a school didn't let students out during a public holiday.

For me, I think this'll work best: access:conditional=permissive @ Mo-Fr 00:00-08:15,15:35-24:00; Sa-Su; PH

...but to each their own.