You know, I never considered a minimum or maximum amount of time one can hold a frog, as I never held a frog longer than a few minutes. Personally, I don't hold it any longer than I have to. Remember, amphibians are not pets that should be held, and this includes White's treefrogs, Litoria caerulea. They may tolerate handling more so than other frogs, but you should keep it to a minimum. I would not exceed more than five minutes of contact time.