Well, presuming you're following Jeff's monthly newsletter for guidance, in it he suggests figuring 30-40 minutes per pound, but since you're splitting the bird, you're actually dealing with 8 lbs, kinda sorta. I say kinda sorta because you have to remember that when you first put the bird (or most any meats you can't let sit on the counter to "warm up" before adding to the smoker), you'll get a chamber temp drop. All in all, your time guideline seems reasonable, however, remember, we tend to preach temperature of the meat as the true "doneness" test, not time. BTW, since you seem to be on a strict time line, you have factored in the rest time at the end, haven't you, the time needed to let the juices settle back into the meat core?