Start with 12/12 and decrease light by 15 mins every other week, so you end at 11/13 or so. Also raise your lights up as the plants ripen to decrease light intensity as well as duration.
Hmm... May have to try a test run on that. But I would imagine there's two sides to the argument one being light is energy that is used in transformation of flowers. Another is a plant can only absorb so much light.