You can do this by using ToD routing. Create a Partition called BusinesHours & a Afterhours. Create a ToD schedule for each one of these partitions. Add these partitions to the correct calling search space. Go to your 246XX hunt pilot and put it in the business hours partition that now has a ToD schdedule associated to it. The next thing to do is create a translation with the same pattern and and put it into the afterhours partition. In the translation pattern add a CSS and send it to your OOH helpdesk.

During hours all calls will go to 246XX hunt pilot. Afterhours the 246XX hunt pilot will deactivate and 246XX translation will activate ad route the calls to OOH helpdesk.

Hope this helps.. Please rate post.