I have a scenario and a problem to solve which can use your brain and experience.
It is an school environment where I am using TOD(Time of Day Routing) to route all inbound calls for a classroom to voice mail during instruction hours. Still I am allowing important School authorities to be able to call that class room even during TOD. This is configured and working properly.
Problem to solve: when there is a 911 call originated from that classroom going out, I need the E911 PSAP authorities be able to call back to that classroom without any problem even during instruction hours when TOD applies. I know the E911 PSAP calling number and I only want based on that source calling number allow the call to go to the classroom. Please let me know if you have done this before and how could this be done.
Is the CSS on your CER systems restrained by the ToD routing rule? Have you checked to see what happens if you apply the same routing controls on your CER system as you have for the "important School authorities". I would check there first.
Since you are using CER, the initial answering point on PSAP return calls should be directed to CER anyway.