Right now I have all calls ring to the receptionists extension. Except a few direct dial lines.
I need for all extensions to ring after 5 PM when the receptionist leaves, so anybody that is after hours can pick up the call before going pt voicemail for the receptionist.
Look into Call Flow Control and Time Conditions. You can send callers to different destinations (e.g. - a specific extension, a ring group, and IVR, etc.) depending on the time.