While visiting a friend in Chicago, I learned that he only steeps his green tea for about 30 seconds. I steep my tea for several minutes because I assumed this would suck most of the antioxidants out of the green tea leaves. He does not like the bitter taste of the longer steeped tea.
I looked into it and found out that you can decaffeinate tea by steeping it for 45 seconds, pouring out the water and steeping the tea for drinking as usual. This will eliminate 80% of the caffeine while retaining 95% of the polyphenols. You can read much more about how tea is decaffeinated here.
I might be able to inversely assume that my friend is leaving 95% of the polyphenols in the tea by steeping it for the short period of time.
But by looking further I found that "tea with caffeine has slightly more antioxidants activity" and that you should "steep tea leaves or bags in hot water 3 to 5 minutes to thoroughly release antioxidants" at aumtea.com