m0useanswered grow question 1mo ago you can't,,,, if they autos they are on their own timeline and will finish when they finish.
Photoperiods will do better on a 12/12 cycle as that allows them to enter bloom. they can not flower under 18/6 the dark period if not long enough. mostly need at least 10hrs uninterrupted darkness. some need 11, 12/12 is just safety/buffer cover all bases, its the darkness that causes it to bloom. Build up a hormone in its downtime that is light sensitive and gets destroyed in lights on time. then takes a bit to get back into motion. why darkness uninterrupted is key.