There is much argument on the "roots grow in the dark" thing...
But I have raise plenty of plants in 24/0 and they all developed roots...
I keep my mom light at 18/6 just to save money and keep the plants a little closer to flowering than 24/0...
The whole "flowering hormone" is not very well understood even by the botanists.. but.. one way I was explained by a botanist and it made perfect sense was...
The plant creates this "flowering hormone" during the dark hours... and it dissipates during the light hours...
So a plant will flower when it has enough dark hours to allow it to accumulate...
If you give a plant 18 hours of dark, it will start building the "hormone" much faster... but growth will be stunted by the lack of light...
So it was experimented with and found that MOST Cannabis will accept 12/12 as a general guideline for flowering...
But of you grew one strain only and got to know it in depth... you could totally fine tune your photoperiod to suit that specific strain.... we're talking YEARS of experimenting to maybe prove I was wrong..
But I do believe that...
And I should also note that they are not "hormones" at all.. there is a mile long name for it... but it is not well understood...
Hope this helps...
Boy I'm stoned...