I always forget to start my preheat and I don't have a regular schedule. I also think the LEAF app is too slow/convulted for something simple. I started with the LEAF_Carwings_EasyAccess github project that gets you a URL which can perform basic actions. Then I connected this big red button to an io-bridge which goes to that URL when you push it.
Tips: Don't forget to use a pull down resistor on the io-bridge digital input and calling the carwings API too many causes it to stop working.