This might be a regional variation for how people are imagining this - I agree with you, living in a cold environment my furnace takes 2-3 hours to get the house up to temp, even longer in extreme (-30) cold, and will still have prolonged on/off cycles after the house heats up so that it's pretty much guaranteed to still be running in case of a staggered start. Warmer climates might be able to get things heated up in less than that hour.