Preheat the oven to 425°. Season the chickens all over with salt and pepper. Stuff each chicken with a lemon and orange half, 2 garlic cloves and 2 sprigs each of rosemary and thyme. Tie the legs together with kitchen string. Set the chickens in a large roasting pan and tuck the remaining garlic cloves and rosemary and thyme sprigs between the legs.
Roast the chickens for about 1 1/4 hours, or until an instant-read thermometer inserted in the thickest part of a thigh registers 165°. Let the chickens rest for 10 minutes before carving.