So what you want to do is disable Automatic Voicemail Coverage for Ext. 10, and re-record your Night Greeting to say "Thank you for calling, blah-blah-blah, this machine does not accept incoming messages". Maybe even wait a bit when recording after the message before you press 1 to end it, giving the caller extra time to hang up before it times out. And, make the Automated Attendant only answer in the Night Mode, add a Night Service button to Ext. 10 if it doesn't have that already.

You press the Night Service button before leaving for the day. Calls are answered by the auto attendant, if the caller presses 0 or nothing at all the call rings at Ext. 10 until they get tired of listening to it ring.