is flowering time based on time since 12/12 or time since first preflower?

For example, does 4 weeks flowering mean 4 weeks since the light schedule was changed or since it first showed pistils

Gabriel said it perfectly

....imo, if your flowering ladies are from clones, you can expect to harvest according the the approx. time given by the breeder. However, if you were to flower form seed, I would not expect to have amber trichomes going by the breeder's estimated time.