Dear teckyuen,
Digital receptionist is a feature that answer the call automatically and serving to callers a menu of options to route the call, so in your case you wanted the call of the specific hours (lunch hours) transferred to a specific prompt and tells to callers 'Please call back after 2pm'.
You have another option, you can create a dummy extension then route all calls from the sip trunk to that extension and on the forwarding rules you have the option to apply your rules at the exceptions box. (Calls/ReceivedTime/ForwardTo).
Please let us know if it works for you.