I feed my autos veg or growth feed through vegetative stretch and well into flowering stretch. I feel that fast growth to get large plants requires nitrogen. In my current grow I switched these to bloom nutes on day 45.
I just use Megacrop from start to finish. I have used just General Hydroponics Maxibloom on autos from start to finish in the past with good results. Maxibloom is pretty close to the Lucas Formula.v