I think I read on a BC Hydro site that dropping the temperature by more than 1 degree Celcius for every 2 hours actually ends up being a waste of energy; as the system needs to work that much harder to recover.
So if your "overnight" period is 6 hours; dropping it more than 3 degrees is a waste. However for myself during the day, that time period is 10 hours for me; so I can drop it by 5 degrees.
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