With Time of Day routing, you don't really have any options here for ringing the DN's that are subject to time-based routing on the fly. Depending on the type of phone (i.e., you need to support at least 2 lines) you have in the classrooms, I would say your best best is as follows:
Add a second line that is in a partition unaffected by the Time of Day routing rules. I'd likely make it a shared line across all classrooms and designate that as the internal "emergency number" that administrative personnel dial to reach all of the classrooms. Whether that works for you or not would be based on requirements (i.e., do you need to be able to ring a single room or just simply indicate an emergency system-wide).
Hailey
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