Just to clarify, I flip nutes when I notice most or all upper growth stop.
That is usually well after week 5 for most auto varieties currently on the market.
During your "preflower stretch" it is not uncommon to experience 1" of growth or more a day.
during this stretch phase, you will generally see a consistent upward growth, if it .5 inches a day or 1.75 inches a day, it will stay fairly consistent if you have things running smooth.
When it starts slowing significantly it is about done with upward growth and you can go ahead and flip to flower nutes without concern over yield.