I cook butts unwrapped at 250 until the IT reaches at least 195, preferably 200. Check to make sure the bone wiggles like a loose tooth; if it does, off it comes. The cooking can take anywhere from 9 to 14 hours, depending on the size of the butt, how diligent I was at keeping the temp steady, and how ornery that particular hog was. After a half hour rest on the counter, it's ready to pull, chop, and serve. Perfection every time.
If it happens to finish early, I'll put it in a pan, cover with foil, and hold it in a cooler. But I avoid this step if I can because I don't like to soften the bark.