Timers - Jumper T8sg Plus V3

My first request for assistance so I hope I'm in the correct category, and I have tried to search. It seems so basic but I'm lost.
Setting up some Blade heli's I have and I want to set a couple of timers. I think I have the battery/fly time Ok starting/stopping with Throttle. However I also want to have on timer 2 a standard countdown timer for the TX. Say 10 minutes. I would like it to commence with the on button and regardless of whatever I fly or do to the Tx it just counts down. I'm happy to set it with each model. Really its for a reminder that I may have not switched off the Tx. Happy to use the same reset switch as the battery on Timer 1.
Any help would be appreciated.

You can set power on in transmitter config settings. See section 8.1.2 in the 7E/10/12E manual link at the left.