Sub never reported during TO

[slow whistle]

This is sort of a fine line though no? At what point do you penalize? Say they are breaking the timeout huddle and the illegal sub gets halfway to the free throw lane and remembers that he didn't report so he goes to the table (and would have to stay until next opportunity to sub)? Is he illegally on the floor then? Or are we saying that once the official is ready to administer the free throw, between that point and the time the ball becomes live, there is your window to penalize?