From the day you plant the seed. Tho I find what they list, for the most part, are about 2 weeks off. I have had some dinafem critical jack that fished from seed in 56 days. But don't be surprised if they take 70+days.
autos will upt to 12 weeks if you plant in a huge pot and have th right lighting...but for the most part most you can grow them to what they are advertised as if you grow them the way the breeders grew them....plant on 6-8 weeks for most autos
I start counting from the time the plant shows it's first true set of leaves. And the timing of a plant can be spot on or several weeks off of the breeders predictions and it can vary from seed to seed. Good luck