Before I had a DO meter, I was trying to figure out appropriate oxygenation times, and so contacted Wyeast for more details on their oxygenation experiment. On their
website, they show different levels of oxygenation that can be achieved with different methods. They said that 12ppm can be obtained using pure oxygen for 60 seconds, but they didn't specify the flow rate. Greg Doss helpfully responded to my question and said that, for these experiments, they used a flow rate of 3.5 LPM through a 2 micron stone.
So, to oxygenate 5 gallons to 12ppm, you would oxygenate for 60 seconds with a flow rate of 3.5 LPM using a 2 micron stone.
If you don't have a DO meter, your best bet is choose a consistent method of aeration/oxygenation and then vary your pitching rate in order to achieve the desired results (since, in general, oxygenation and pitching rate interact with each other to produce the total amount of yeast growth).