Let's take a thermostat what does it do? It is a simple machine which has make the temeperature as you want in particular time.
In simple words you want to have a proper temperature for proper time and thermostat has to ensure it.
How this time is measured you may ask. So I am answering you now we measure time by date, hours, seasons and operations (?? by the way I will never understand why operation is a time).
Season depends on current date on individual Earth area. Operations depends on day time in other words operation depends on hour of a day.
Date is combination of day and month as well as today is always some date.
In conclusion in thermostat temperature is set by setting thermostat_settings in degrees. Those settings may vary on operation and season.