Mine is a Florida Kingsnake, and I imagine the needs for brumation are different for a Florida than for yours. I cooled his temps until the under the tank heater was off. I did this slowly, over a week or more. The room is in the low 60's. This seemed fine for him, he settled down and was inactive for about eight weeks. But again, I am sure the needs of speckled kingsnakes are different than the needs of a Florida.
Sorry I can't be much more help, but the main thing is to cool it down. It will burn up too much energy with the warm temps.