My domestic water heating needs around ¼ hour a day with a 19 kW boiler, but the thermo syphon needs around ½ hour to get going, I have no tank thermostat, so only option was ½ hour every other day, so to be able to set it needs a timer with a week not day timer, so my old mechanical timer
was replaced with an electronic one, in my case Nest Gen 3, however for an immersion heater with a built in thermostat at only 3 kW not 19 kW then 6 x ¼ is an hour and a half, as I found out, once hot the cylinder stays hot for over two days, so only reason for a timer is to use off peak power, OK there is an exception, the Willis system, but that is rare to find on mainland UK, only the Irish seem to have worked out how to use it. We are too tick.
However we have no idea what the timer is used for, I use timers for Christmas lights, and internal lights, mainly see to turn them off should we forget, and I use many different types, some also monitor power used, most in some way connect to the internet.
Although the plug in timer rated at 3 kW not sure I want to use it with 3 kW, and some I use are rather limited, the sockets only have three on/off slots per day, you can select which days of the week they are active for, and also can use IFTTT to get more and clearly are good for 13 amp.
However we have no idea as it stands what the timer is for. I would modify my suggestions depending on what it is used for.
