1Heat oven to 375°F. Generously spray large shallow roasting pan with cooking spray.
2In cavity of each chicken, place 4 thyme sprigs. Rub chickens with softened butter. Tie ends of legs together with kitchen string; tuck wing tips under. Place chickens, breast sides up, in roasting pan. Squeeze lemon over chickens. Sprinkle with salt and pepper. Insert ovenproof meat thermometer so tip is in thickest part of inside thigh muscle and does not touch bone.
3In medium bowl, toss garlic with oil. Scatter garlic around chickens, placing cloves close to chickens. Bake uncovered 1 hour 45 minutes or until thermometer reads at least 165°F and legs move easily when lifted.