Yea this 12/12 cycle is just an optimum. We are trying to improve on nature remember. It makes sense to me that in nature you may have a dark period of over 12 hrs every so often. There may be major clouds for a day or so and the outdoor plants deal with it. But if the sun was out for 24 hours straight the plant may have a problem dealing with it. Wouldnt you. So I agree with Zandor It just make sense not to put a plant in a enviroment that it would never possibly experience in nature.

So in flowering
12+ light period = Bad
12+ dark period = OK
but not multiple times will stress.
Sweet Leaf Dreams