The time turkey breasts (or anything else for that matter) is relative to the smoker temperature, and the cooking characteristics of that particular smoker and the particular cut of meat you're smoking.
30-40 minutes per pound would be about right, with the smoker at about 250 degrees. The smoking times suggested are just a general guideline.
Always use a meat thermometer, and use it to decide when the turkey breast is done. When it reaches 165 degrees, it's time to remove it from the smoker. Let it rest for 10 minutes before serving, for maximum juiciness.
