Hi Clay,
One thing I just thought about is that acetone is a bit hydroscopic, which means it absorbs water from the air, so keep the jar covered with aluminum foil, the lid, or something else to keep the air that can get into the jar, to a minimum. You don't want water that the acetone absorbs to swell the wood. Because of the potential of water in the acetone you may want the knob to come to a stable state with your climate again before you refinish it. I would guess it might take a week, but others on this site would know better than I do. Ordinary solvent grade acetone sometimes has a little bit of water in it, even a new can, but the amount should generally be only a tiny amount.
Stew