I don't think I have some master thermostat.

Well, spend your money having one installed, rather than fixing the clock.

P.S. Also, put TRVs on all your radiators, too, except for the room you
choose for your room thermostat. I prefer the lounge for this, as you get
tightest temperature control in the room selected. Some choose the hallway,
as it is often the coldest and most underheated room, so the heating stays
on until all rooms are hot. However, you mustn't choose a room with
alternative heating (such as a fireplace or gas fire) that is used
frequently, as it will fool the heating into shutting off, making the rest
of the house cold.

Doing all the above will not only save you (and the earth) a bomb, but will
actually improve the comfort of your home.

Christian.