It occurs to me that, given the philosopher's stone is around, any superweapons Harry could create and conceal with it in slightly under an hour could exist in the clearing, provided that they're enough to let Harry survive another hour, access the time turner, and create said superweapons.

Also, since prophecies are self-fulfilling and Voldemort prefers a world that won't end to a world that will and Harry has already made the appropriate unbreakable vow to do everything to prevent the end of the world, Harry could argue that expected universe where Voldemort lets Harry live is far superior to the one where Harry dies.