Nope. It's your schedule of when to add the hops to your beer. I'm assuming you're using a kit that has a total boil time of 60 minutes (or 90 if a partial mash/soak kit). So, set an egg timer or the timer on your oven/microwave to count down your total boil time. You add the 1 oz of cluster at minute 45 (out of 60), the williamette at minute 30, then the mt hood at 15 mins before the end of the boil.
Hope this helps!