The information about the hormone is wrong. Phytochrome has two forms. It is a pigment that initiates the release of a hormone when it transforms from Pr to Pfr--this stand for red light and far red light. Far red light (what is seen mostly by the plant just before night) converts the Pr (this is the inactive form) to the active Pfr form. This form of the pigment enter the nucleus and tells it to code for Florigen (a protein that is a hormone just recently discovered). Red light converts the active form of Phytocrome (Pfr) to the inactive form, Pr. This process takes a while for enough Phytocrome to enter the nucleus and cause Florigen to be created--this is why the dark cycle is required. Thus dark periods are required until enough Florigen has built up. This is what that guide at a1b2c3 eluded to--however I do not think it was written with the knowledge of the newest science.