I recommend that the light hours be 12. You should also make sure that during the 12 hours of total darkness there are no light leaks. Many times plants don't flower because they don't receive enough hours of darkness. During the light period, there are 2 main receptors balanced in quantity, the red phytochrome and the far-red phytochrome. In the dark, the far-red converts to red. The increase in red is what triggers flowering.