Currently, the U.S. Postal Service considers a first-class package late if it arrives three or more days after it’s posted. The service is in the process of moving more of its package deliveries to ground in order to save on air transport costs. The move will necessarily result in slower package deliveries overall, and so the USPS is resetting its standards so that 30 percent of first-class packages will be seen as “on time” if they arrive within four or five days.