have always waited until buds are like little cherries then change to flowering nutes that was with feminised and ordinary seed, would think autos are the same
plant apparently cannot take the different npk ratio until then do not see why auto should change things.
I learned with autos that when you see the first pistils flowering is coming in a week or less.
I usally start flowering nutes together with grow ones when the firsts white pistils appears and stop grow nutes after 5 days. Good luck with your grow 💪🏻👊🏻