In Ann writes:

It's the old question of night-time furnace setback. Only longer. It
does save energy.

Yes, it does. And turning it off entirely at night would save even more.
I tried that for a while this Fall and the colder it got, the longer it
took to get the house warmed up to where it was approaching comfortable.
And there was a strong temptation to set the thermostat higher than normal
to get it to stay warm sooner.

Ummmmmmm...... except in a very few cases with specialized
heating systems [a], moving the thermostat to a higher temperature
isn't going to speed things up.

[a] multi stage furnaces/boilers, and heat pumps with
additional resistance or fossil fuel input.

But it does look like in your case there wasn't much to warm up.


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