~1400 Sqft House uses propane to heat it up. Does it use more propane to heat up the house or leave it at a constant temperature.

Hello, first time homeowner here. My house uses propane and at night here in the southeast it gets down to about 30 degrees lately. I've been leaving my thermometer on 45F at night and then heating my house to 65F when I get back from work. So during weekdays, the home is only heated/heating to 65F for about 6 hours a day and remains at 45F for the other 18 hours. On weekends, the home is heated to 65F for about 14 hours a day and remains at 45F for the other 10. Does it use more propane to constantly have the house reheated to 20F or is this method saving me propane? (Personally I enjoy sleeping in a cold 45F house at night)