FWIW I have experimented with O2 injection flow rates and time using pure O2 and a flow meter to maintain flow rate. A flow rate of .5scfh and a duration of 3 minutes gave normal attenuation level with a ready to pitch yeast vial into 6 gallons of 1.055 wort. More duration and the attenuation went up significantly, more flow was a waste as if it makes foam, it is not absorbed into the cold wort. Most dramtic result was 5 minutes into a 1.045 special bitter wort, it fermented to terminal gravity in 36 hours, 20% loss in foam through blow off hose, and finished at 1.001. All the testing was done without starters, just shake and pour ready to pitch vials/tubes of ale yeast to keep yeast cell count variable relatively similar, worts were 1.055-1.060 range and batch size was 6 gallons.