I thibk the transition week counts as flowering week already, sometimes is hard to tell what is happening when growing autoflowers but with photos, once you switch to 12/12 you are in flowering state.
But nutrient schedule wise, usuallt you wait a week or 2 to start bloom nutes, and if that is the case, then you start counting the first day of flower once you switch, or if its auto, you wait for pistils, and when they show up its usually after that 1 week or 2, hope it answer3d ur question.
If you want to contribute back just don't forget to pick an answer as THE ANSWER, because it helps me or another one to get 1 more point in the contest to win a couple seeds and a small ammount of merch, like a tshirt a poster and a grinder.
Thanks and best of luck growmie