Ed Huntress wrote:

The confounding issue, though, is the thermal mass of the house. That's why
the DOE explanation says that the savings occur when the temperature inside
the house has stabilized at the lower temperature.
Yes, if the house has only dropped a couple degrees when you get back,
then there's little benefit. if the house cools rapidly to the lower
temperature and stays there for, say, 7 hours before you return, then
you get a benefit. Of course, if your house cools off very quickly,
then you might do best to invest in insulation.

We had a big ice storm a couple years ago, and found we could be
moderately comfortable for about 8 hours before firing up the generator
to bring the furnace online. I think that means our insulation is doing
pretty well.

Jon