Happy Thanksgiving to you all!
Barbara Kafka says a 20-pound unstuffed turkey will take 3.5 hours: http://www.bkafka.com/Recipes/roastturkey.html
Yes! It should be *about* ten minutes per pound at this method. (Oven temps can vary a bit.) I would make sure that you tuck the wings to prevent them from burning.
Sweet! Thank you!