My dad is on a electricity plan that provides a cheaper night rate of power between 9pm and 7am. So he now turns off the hot water cylinder out side of those hours so it’s only heating during the cheaper night rate.

My argument is that Surely it’s more energy efficient and therefore cheaper to keep it at a constant temperature 24/7 rather than having it cool right down and have to work over time to heat back up at night.

Any thoughts?

TIA.