You are aiming for under 12 minutes here; a very annoying task. There is a trick to this though that saves you the money from buying the double jump. There is a split second pattern of timing the jump button twice in order to complete a double jump without having purchased it. Without this trick, your run will be much closer to the wire, rather than 30+ seconds below. Practice of this timing is really difficult but if you can do this on command it will pay off. The attached video is my runthrough of the game, making use of this double jump trick.