Assume 1 1/2 - 2 hours per pound. But time is worst means for deciding if it's done. If you have doubts or are just starting, use an instant read or probe thermometer to verify. (Remember it won't hurt if the meat goes to 205*.) Best of all, stick in a probe (thermometer, skewer, etc.). If it goes in easy, try again in another area. If it still goes in easy ("they" say like butter), it's done.
Be sure to let it "rest" for at least a half hour before "digging in". The temp will continue to rise probably another 5* or so.
Rich