To be honest.. most people I think of as actual 'growers' (not commercial guys who try and keep a scheduled harvest) I consider growers, quit keeping track of calendar dates long ago.
While excellent for new growers to have a general idea, a seasoned grower (who is growing for himself) will just read the plant and wait until the fruit (flowers, whatever) are ripe. Rarely does this happen around the time they say on the package.. heh.
Just 'feel' and read the plant and realize you hit on it yourself, there is no 'standard'.. one persons 12 12 starts the second they flip, another starts when it is developed more. Breeders tend to go towards the 'flip' time, but they REALLY MEAN the after it is developed time.. or rather, commercial sellers/breeders seem to have an almost sophomoric need to demand the darn things will grow mature faster than they do.
For the record, when I'did' count, it was always well after flip after it shot out actual beginnings of flowers. But that was just me, there are no standards.