Thanks to the pointers provided in this thread, I was able to reconfigure the night service routing as desired.

I gather that if there isn't an entry in the DID table for the night mode, the routing continues to use the DID routing for the day mode. What I found was that in one case the night mode route was directly to 600 (VM), while for another DID number the night mode routed to a virtual extension. I assume this was done to allow that extension to have a different greeting message for calls received after hours and that with the right VM tricks the actual recorded messages could be combined in one MB.

I'm still not sure I know where to look to find the mapping that links a night mode (Aspire M has 8 total) to a DID routing table. Is this something I can change or is night mode N always associated with DID routing table N?