I have a recipe that calls for slow-roasting a 5 - 6 pound Boston butt pork shoulder at 275 for 4-6 hours. If I want to half the recipe to a 2.5 or 3 pound roast, how long should I cook it for? Also, 4-6 hours is quite a wide range... how will i know it's done? I have a meat thermometer, at...