adding acetone extends the cure time to several days or several weeks, depending on how much you used. there was a recent thread of someone doing this to pot a heating element, and who went to use it after 24-48 hours. the tread was to ask why it kept tripping his GFCI, and the answer was because he didnt wait until the expoxy was set.
before you use it, make sure that its completely set. it should be a rock, not rubbery at all.