Cut 12 garlic cloves in half. Place chicken on a cutting board. Tuck wings under chicken. With a sharp paring knife, cut 24 small slits in breasts, drumsticks and thighs. Insert each with a halved garlic. Place the lemon wedges, thyme and remaining whole garlic cloves in chicken cavity. Tie drumsticks together.
Transfer chicken to a rack in a shallow roasting pan, breast side up. Rub skin with butter; sprinkle with salt and pepper.
Roast, uncovered, at 350° for 1-1/4 to 1-1/2 hours or until a thermometer inserted in thigh reaches 180°. Remove chicken from oven; tent with foil. Let stand for 15 minutes before carving.