In a small bowl, combine the salt, paprika, onion powder, garlic powder, thyme, black pepper, & cayenne pepper. Remove and discard the giblets from the chicken and rinse the chicken cavity. Pat dry with paper towel. Rub each chicken inside and out with the spice mixture. Place 1 onion (quartered) into the cavity of each chicken.

Place chickens in a resealable bag or double wrap with plastic wrap. Refrigerate overnight, or at least 4 to 6 hours.

Preheat oven to 250 degrees.

Place chickens in a roasting pan. Bake uncovered for 5 hours, to a minimum internal temperature of 180 degrees F (85 degrees C). Let the chickens stand for 10 minutes before carving.