People count from flip or the beginning of flower. I just count from the flip to 12/12 to keep it simple. As long as the plant is mature and ready to flower I think it just makes it easier. If you grow a plant from seed on a 12/12 schedule than I would count it from when they started growing flowers though. You can never go by the breeders time. I'd add 2 weeks or so to their suggested harvest time, but it also depends on how healthy they are. Yours are looking great, so the 2 week rule should be somewhat close.
It's better to harvest late than early.