Magic Mushroom Question?

How long after first ingesting magic mushrooms can you take more? I have wasted 2 hits of acid and an eighth of shrooms before. From taking them too long into my trip. I just got some shrooms from chicago that are supposed to be better than the ones where I am from. I got an eighth, I am planning on taking half now, and half later. So how much later can I take them and not have them go to waste?