I have to disagree, flowering starts when your plant starts showing preflowers "electrified puffs", this would be the appropriate time to change to bloom nutes. You would stay on veg during the first few weeks to give the plant what it needs for stretch, once the preflowers start to show you want to start giving bloom and reducing your veg nutes (depending on your nutrient schedule ofc).. counting from this point will also get you closer to most breeder estimates but def don't count on the breeder times, those times are just in their garden not necessarily in yours.