It all depends on the strain man.. 12/12 is just a general guide line all strains will flower at.. The more light you can give a plant while it's flowering the more energy the plant has to put into the bud.. Most outdoor plants normally start flowering in the middle of august, when the light is roughly 14/10.. Last year my plants finished the second week of October, the light was still longer then 12/12 when I chopped them.. The trick is to allow the plant to get as much light as possible, while still allowing a long enough dark period for the flowering hormones to build up to the critical levels needed for flowering.. The shorter the dark period the longer the plant will take to flower though. I'd probably start slowly so you dont mess up the light cycle to bad.. When your ready for them to flower, start covering them up after 13.5 hrs of light.. Then step it down by a few minutes every day, untill you get to 12/12. I would also make sure to uncover them before you went to bed at night. That way they can catch the first rays off morning sun...
