Hysteresis 0.2, 0.3, 0.5, and 0.7 are how much the room temperature has to drop beneath the set temperature for the thermostat to tell the radiator to heat, in ˚C.
So, if you select hysteresis 0.2, the thermostat will tell the radiator to heat when the room temperature drops more than 0.2 °C beneath the set temperature.
So, if you select hysteresis 0.2, the thermostat will tell the radiator to heat when the room temperature drops more than 0.2 °C beneath the set temperature.