I have looked at switching things on automatically be it water heating, central heating or even just a fan.
However it does not work as well as you think. Rooms, tanks of water take time to heat, and cool, so turn off heating leave for 24 hours and you find it has only cooled a few degrees, we have done so much to insulate it becomes pointless to turn off/on. Unless something like ecommony 7 is used.
Years ago my dads hot water was heated by the central heating boiler and there was no tank thermostat, the boiler would cycle unless a timer was used. The tank would cool down to near ambient in 24 hours, great for airing cloths, not so good with fuel costs. You could add all the jackets you wanted, it still cooled down, but today it has all changed, so be it a programmed TRV or a timed immersion heater, we need to think again, is it really worth it?