That was the first thought but you would need an adjustable TD relay and it would be one more thing they would have to be messing with all the time.
I have some timers that use an electronic clock that will run years on a 9v battery but I can't find one that actually supports anything but a 5-15 and this probably needs to be in a 3R box. I guess if it is small enough it could be in the hand hole.
