Whisk vinegar, mustard, oregano and thyme to blend. Slowly whisk in olive oil. Stir in olives and season to taste with salt and pepper.
Place hens or chicken pieces in sealable plastic bag and pour in marinade. Seal and refrigerate several hours or overnight.
Transfer to foil-lined baking dish. Pour marinade remaining in bag over hens/chicken. Bake at 375 degrees about 45 minutes or until done.