Easy peasy.
Point each DID to it's own hunt group during the day, with the operator as the hunt group member. Recall to the appropriate Call Routing Application for the specific dealership.
As to no operator being available during business hours, this will take a little more effort. As you pointed out, there is only one night mode. You can't use DND to control multiple call forward paths that would be needed for the DIDs. Point the night Calling Routing Table to STAR applications, one for each DID. Build a table for business hours, and make the default routing the night application.
When the operator isn't available, put the system in night mode. The STAR tables will determine if the day or night message will be played.