Thanks for the info! I got help. I created another mode and set up an answer table. Calls to the main number are now being sent to a newly created transaction box from 1:00 to 2:00PM on weekdays. The transaction box plays the lunch greeting and gives callers an option to dial 9 for the answering service, sending the call off-premise. I copied the appropriate 1-key dialing setting. Had to be careful that schedules in the phone system didn't conflict with schedules in the VM system, since the opening box was left alone.
Cheers to you both for replying!