I've found that it's a good idea for peak aroma to wait until the beer's at FG & has settled out clear or slightly misty,then dry hop one week. If you don't wait for it to clear,the hop oils will coat the settling yeast cells & go to the bottom. You want the hop oils to stay in suspension for good aroma. Some folks think dry hopping adds to the flavor as well. But that's only because our sense of smell is linked to our sense of taste through the roof of the mouth. That's why dry hopping works so well. It's perfectly linked to both of those senses.