Need help with a routing request

[pmterp]

I have a client that does not use voicemail at all. During business hours (9a - 5p) calls ring a ring group until answered (nothing ever goes past 180 seconds). Outside business hours calls are sent directly to an off site answering service.
Simple so far, but here are the 2 variables that complicate things:
1) From 8:00a - 8:59a & 5:01p - 5:59p they want calls to ring the ring group first and then if not answered in 20 seconds calls go to the answering service.
2) Occasionally they will leave early or take a day off (Thanksgiving) and want the ability to switch to the outside business hours routing (have calls sent straight to the answering service).
I can accomplish everything but the 2nd part by using a dummy extension's forwarding rules and defining time intervals to forward calls to two separate ring groups. I'm just struggling to find a way from them to manually switch it to the outside business hours routing that will automatically switch back the next business day.
Any suggestions would be appreciated.

 

[StefanW]

there is a force out of office dial code, check the admin guide for more information reg. dial codes. Does this help?

 

[pmterp]

there is a force out of office dial code, check the admin guide for more information reg. dial codes. Does this help?

Thank you @StefanW that could be useful. However, I'm assuming there is no indicator on the phone to let anyone know that it has been switched, correct? So if for example the receptionist left early on a Tuesday and dialed *642 (assuming I set the *64 code), unless she lets someone know to dial *64 in the morning, calls will continue to be routed to the on call service.
This is better than no solution but I'd love a way that would automatically switch it back once office hours resumed.

 

[StefanW]

once forced - it will force until force switch or set back to auto.
There is no phone indication on this feature.