56 days is just a guide, usually really an advertising hook to sell their seeds, by under cutting the opposition by trying to make people think that their strains are uber quick. 56 days may be right for a particular plant growing in the perfect environment in a breeders super dooper grow room. However, seeds being unique organic living beings, each and every seed will be slightly different genetically, from the other seeds coming from even the same mother plant. 56 days does not take into account your growing methods, your lighting set up, your feeding schedule, the temperatures of your environment etc. that makes 56 days nothing but a rough estimate. Therefore, with all these variables and with slight genetic differences between seeds, your plant will be ready when she is ready, and not what it says on the packet. You will have to judge when she is ready and not be too concerned if it is 51 days or 77 days, your plant holds that answer.
There is plenty of information on this forum about judging harvest timing, especially in the Grow Diaries Journal/Blog section that can be found listed on the home page.
Hope this helps,.... Organoman.