|What time frame does|
|Plant tag instructions can sometimes be confusing so I'll try to sort things out for you. First of all, don't fertilize your pieris immediately after planting. Most landscape trees and shrubs go through a little transplant stress and need to concentrate on establishing their root systems rather than trying to grow new foliage. Fertilizer generally encourages new foliage - so hold off on the fertilizer for 5-6 weeks. As for watering, pieris are quite adaptable to soil conditions and moisture levels once the roots become established. So, for now, and all summer long into fall, water your plant on a regular basis. It will require about one-inch of water per week, applied slowly so it has a chance to trickle down and wet the entire root mass. I think the easiest way to accomplish this is to build a soil basin beneath your new pieris by mounding up a few inches of soil about 12" from the trunk or main stem, all the way around your shrub. Flood the basin with water, allow to drain, then flood it again. This method will concentrate the moisture directly over the root system.
Hope this clarifies things for you.