yea i'd keep watch over him. he should be alright if he just sits in the shallow end and moves around every now and then.
ha, and if he did it in the deep end, i bet he'd make it a little over an hour. I tried just jumping in fully clothed into the deep end of our pool, and was able to tread water for about 90 minutes. In a bathing suit it was about 2 hrs, and it gets really really tiring very quickly.