Personally i would grow a couple and harvest at different times to see what works best with your enviroment. From my experiance hell no all dates are off clones and seeds.
can vary alot on your setup, usually the pro breeders wont be using say cfl's, which take an extra couple weeks to finish a plant alot of the time personally i use the dates/times they give as a very basic guideline when shopping for seeds, but then just harvest by checking the triches
Under IDEAL conditions the indoor time they give will be accurate. I've seen outdoors go an extra 3 weeks.
Scoping the trichs is the only way to tell exactly what you are getting!!!!! Overall the times are 7-10 days off of claimed results, due to differences in grow conditions.