I usually set mine to 19C (66F) based on the sensor in my hallway, but it's rare it will actually reach that temp upstairs, meanwhile it will be like 17C in the living room. So I usually manually turn it off when I'm comfortable. I never let it run when I'm not home, but I might start it from work an hour before I head home just so I can walk into a cool house.
Generally I try to tough it till 7pm though since that's whene hydro cost is like half the price of during the day. This is where a solar setup would be nice to have as I could generate my own power at peak of day. Need a pretty serious inverter to run a central AC unit though.