Time sounds right on the money to me, Steve! I never experience any kind of a "stall" with poultry, so it usually goes pretty fast at 250°. The stall is from evaporative cooling on things like briskets and pork butts, as the fat/connective tissue renders and flows to the surface, cooling the meat much like our skin cools when we sweat. Poultry is extremely lean, so that doesn't happen. Typically, you'll see a steady climb in temp with poultry.
As for your question on the mire poix (chopped celery/onion/carrot mix) - try it some time in a chicken or turkey. I always use it on whole birds, since I learned about it here, on the forum. I think it helps the meat cook more evenly, and gives the meat a great flavor.
