There are two methods you can use to accomplish this configuration:
The first method is to use Time of the Day (ToD) routing in Cisco CallManager 4.1.2 or later so that the call is routed to a different call handler based on the schedule setup in Cisco CallManager. Refer to Time-of-Day Routing for more information on configuring ToD routing in Cisco CallManager.
The second method is to use Cisco Unity to pass a call handler to another call handler when someone calls after hours. Complete these steps in order to accomplish this:
Create two call handlers. For this example, one is called "staffing day" and the other is called "staffing night". The staffing day call handler is where the call first goes to when it gets passed to Cisco Unity.
Create a schedule called staffing day, and check the boxes that represent a regular working schedule. Save it.
Assign the schedule to staffing day in the Profile section.
Go to the Greeting section in staffing day and change the status to Closed.
Make the greeting blank.
In Send call to, choose Subscriber and specify staffing night.
Save the changes.
This passes the call to the after hours call handler during the after hours time frame. Refer to Call Routing in Cisco Unity for more information.