From my experience, seems like the plant hits a peak nutrient usage around 6 weeks in...
So by the 6th week of flowering I am feeding it the strongest. After that 6th week peak feeding I start backing off, lowering my mix until near the end when I no longer need it. At that point I give it a good watering, I said 10 days earlier, but really for me its 1 week prior to my estimated cut date. I always see a spurt of new growth after the 'flush' so if it stresses it, I am not sure how. By the time the water dries out in the soil (which is always 4-5 days) its almost cutting time, so I dont water it, throw it into darkness and cut it 48 hours later.
My leaves are still green when they come out of the 48 hours of darkness. Sometimes they are still standing up straight, sometimes they are drooped over.
I have done both ways with the same strains several times no flushes, no dark period. To be completely honest I cant tell much of a difference either way. Doesnt seem to hurt it at all, not sure if it helps it at all. Scientifically they say that thc is highest during dark cycle, so I will continue my 48 hours of darkness either way. Since the flush doesnt hurt it at all, I will continue to flush it. It certainly hasnt hurt it at all.