Increase Ring Time Without Connection

I would like my extensions to ring for 10-15 seconds prior to going to voicemail even if there is not an active sip/webrtc connection. How can I do this? I have been looking at creating a custom context but cannot seem to get that to work and the call goes immediately to voicemail if a connection doesn’t exist.

Basically any call needs to attempt to ring for up to 10 seconds. Then go to voicemail if it is still not answered. I have many extensions and all of them need to be handled the same way.