pre-flower would be as you switch to 12-12 or thereabouts.. was it suggeting 6 weeks for an autoflower? That might be ~10 days beyond 12-12 as a rough equivalent.
I don't follow that thought. i feed the same from start to finish.. possibly lighter concentration initially, but only by accident, lol. Happy plants start to finish, and as long as i am religious about 10-20% runoff, don't expect much less.