[osolemio]

Circulation is the way to go - if you have the possibility of make a return pipe, or a full circuit. For a bathroom, all you have to do is connect a timer to the light switch, and then to a small pump.

Whenever the light is turned on, the pump runs for a set amount of seconds, depending on the pipe length. This way, you don't need scheduling, which doesn't work anyway when you sleep late, wake up in the middle of the night and so on.

From you turn on the light until you use the hot water, there is usually at least a minute or more, whether you use the toilet, shower or what. And if the light stays on, the pump stops. The timer is only activated when the light goes from on to off, and then only for a set period of time.

Other places where use of water is not always related to a light switch, a separate switch could activate the pump. Of course you would have to press the switch and wait before you use the water.