24Hrs a day, 365 days a year!
Set on 20.5c only comes on when it needs to. I’m in the house almost all day every day, my only regular time out is for about 3 hours on a Monday evening.
Gas CH and the bills haven’t really been any different when I used to use a timer for it.
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!