As we get deeper into fall, I was wondering what are the lowest acceptable (healthy) overnight temperatures when electing to not brumate?

Assuming when I wake up each morning I will bring the temperature up to the normal recommended range, is it ok for it to be somewhat significantly cooler overnights? I ask because my house gets quite cold in the winter and late fall, especially overnight, and I don't want my garters to end up in some sort of a confused state halfway to brumation.

If more than a very slight drop is a problem, I can always leave the heating pad on all night, or put it on a timer.

By the way, this would be for a pair of Red-Sideds (probably more tolerant of cool temperatures than others).