Cut off the tops of the garlic heads and rub the cut surface with the olive oil. Put the garlic in a garlic roaster or on a baking sheet. Arrange the rosemary and thyme springs on or around the garlic. Cover the garlic roaster with the lid or the baking sheet with aluminum foil. Roast until the garlic cloves are soft and lightly browned, about 1 1/4 hours. Let cool completely.
Squeeze the pulp from the garlic cloves into the container of a blender or into a deep bowl. Add the sour cream, mayonnaise, chopped rosemary, thyme and parsley, the Worcestershire sauce, lemon juice, salt and pepper. Using the blender, blend until well combined. Cover the dip with plastic wrap and refrigerate for at least 30 minutes.