Programmable thermostats have a number of “events” usually 4 or 6 through the day. The timing of each event can be adjusted by the homeowner, both for appropriate time and also temperature.
This means a programmable thermostat is never actually “off” – chosen events can simply be set to a low temperature (for example 7°C. so the heating will only come on at that time if the temperature drops below 7°C.)