If it's from midwest, morebeer, austin or northern brewer, they sell a lot of their stock so the turnover on new product is pretty good. I'd say you have a few months before it starts to go south on you, but i'd use it sooner than later. If it's going to be a while before your brew day, just order in your supplies about a week before your brewing.
Beer so good, it's frightening.
2014: Seven Heavens Series One: Vilon, Mystic Melomel, Skeeter Pee.