If left uncovered, the acetone will evaporate. I use a small glass jar with lid. That's where the delrin bushings go at the end of each day. Ready for use the next morning.
I have to admit, I've never cleaned mine. I frequently get CA all over them, and then have to chip that away. I think that takes most of the stuff that would accumulate on them away. The jar o' acetone solution sounds a whole lot easier.
I made a wire mesh basket that I place in an old pickle jar with acetone and I throw my delrin bushings in that for a few hours. Then I can just pluck the basket out and the bushings are nice and clean.
Have never needed to clean bushings, steel, delrin or otherwise. Not sure how much CA people are using or technique but sounds like way too much to me.