Call Forwarding Timer, KX-TD 812, 1232, 500, KX-TDA1232
Early KX-TD software versions set the call forward timer globally in system program 202. It was set the same for all phones, if set to 3 rings, all phones were set to 3 rings.
The later software versions (I believe version 4 and up) featured forwarding timers that could set by extension in program 612. The problem was it still had to be set in system programming either with a laptop or via PT programming (through a manager’s phone).
Your best bet is to have a local Panasonic dealer come over and make the changes for you.