@dooglus that wouldn't work for our site, as the members do not wait to wait 5 mins to find out if they win. Do you have any other suggestion?
Well, so long as the calculation takes longer than the game I think it's OK. Most games are what, 30 seconds or less?
Maybe your members don't care if the game isn't provably fair. That's fine too. Just don't advertise it as provably fair when it isn't.