The function of the IP Fence is to cover situations where Timed Commands will not execute, example the device has left the company floor/building/network but is still online (using other WiFi source, mobile card, etc.).

In this scenario IP Fence will come into effect - it is online but cannot see the required IP Address.

If there is no network to be seen IP Fence cannot function,  this is where Timed Security would come into effect.