It really depends. I've heard that some need lights to be changed to 12/12, like the super cali haze. I've grown snowryder, russian rocket fuel, assassin, and blue himalaya, and they all finished using 24 hours of light every day.
I hear some need to be taken down to 20-18 hrs of light to trigger it, but their are definetley strains out there that have no qualms about flowering under constant lighting, every once in a while youll see a male from a non-autoflower strain start to flower under constant lighting, although that really doesnt have anything to do with this thread.
I always leave my atuos on 24hr lights and they do flower i do give it 48hrs of darkness before I chop though they really great if you dont want the mess about light times etc
Incorrect....you can "mess" with the lighting on an auto all you wish....they do their thing by genetic code, NOT light periods. I grow ALL mine under 24/0 for a month, then move to a hps system on 12/12....no problem whatsoever.....except perhaps a bit smaller yeild......but I grow for quality, not quantity. I have never done any dark periods before harvest and my autos are dank.....
the 24 or 36 hr dark period is for any plant, it is because thc is destroyed by light, if a plant is not given light its levels can build up to its maximum. its not a magic bullet but its been shown to increase thc in some strains up to 30%.
There's actually a breeder doing some tests to determine methodology of cloning the new "super autos".....no final word on it yet....I believe the breeder is "stitch"....