If you're making a smaller chicken, adjust the seasonings, oil, and cooking time proportionately and cook until it reaches an internal temperature of 165 degrees. (Even if your chicken has one of the little pop-up things in it, don't rely on that to test done-ness. A meat thermometer is much more reliable.) Be sure to let it rest before carving to help preserve the juiciness, as tempting as it will be to dig into your chicken right away. If your potatoes need a little extra time, just pop them back in the oven while your chicken is resting.