What is the most efficient method for heating of rooms on working days?
The engineering theory is that a greater differential in temperature causes a faster loss of energy, so maintaining a constant temperature is more costly. 

This theory was proven by tests of Twin Homes by The Canadian Centre for Housing Technology. Several papers have been written about studies at these homes, here is a rather thorough one https://www.healthyheating.com/downloads/Thermostats/nrcc48361.pdf