Well I don't have an exact answer for you, but I used to live in Hawaii. The sun is very strong there. I never let my daycare children stay out in the sun for more than a few hours during 10-2. If they were in the pool we would reapply after an hour and then they all came in the second hour. When I went to the beach myself, I never stayed more than 3 hours. It was just too hot, sand and everything.
Sorry that wasn't much help.
Sorry that wasn't much help.