My suggestion is to add 2 hours to whatever you estimate your cook time to be. This gives you insurance time against sudden weather changes, longer than average stalls, etc. When the butts are done, double wrap on foil, place in a dry cooler & cover with towels, newspapers, etc. If they get done early, no problem. I have held butts 5+ hours in a cooler & they were still too hot to handle with bare hands. They extra rest actually helps the meat reabsorb juices.
Jim Sewell -- GBA Vice President, Master Judge, Contest Rep & GBA Webmaster