I have heard many things about it too , so I've heard the 7th set of branches things , I've heard it's when the roots are hitting the bottom of the pot and start to settle the plant will flower soon.
What I've experiment makes me says that autos are not on the same "line" when it comes to flowering , some are flowering pretty quick and some are giving you the time to train them , it's mostly genetic to me ( depending on the photoperiodic used for the cross )