I like this one, very simple and intuitive.
https://www.tlc-direct.co.uk/Products/HOE30.html
I'm involved with a sort of village hall, and it means the users can have hot water for the duration of their event, and it will turn off automatically. The organiser or keyholder can turn it on at arrival, or beforehand. Thanks to the thermostat, it stops using electricity anyway, once the cylinder is full.
I got one at home, for when the solar panels are running or my boiler breaks down
Edit
sorry I misunderstood
You meant a timeswitch that will turn on the heat, say, every morning at 7am?
I use an old central heating timer for a towelrail only (rated at 3A) but most timeswitches are 16A contacts. You will need a fused one, or an FCU as well. Immersion timers are usually unfused. Some have rotating dials, and the motor/gears make a soft but irritating noise. For cheapness, there are lots of E7 timers (used) on ebay.
You can use electrical accessories (except plugs and sockets) in a bathroom as long as they are outside the zones (not close to a fixed bath or shower) and not liable to have water dripped, splashed or sprayed on them. Or you can put the timer outside the door.