Between any two cities in the continental United States, a letter, parcel, or package of almost any size can be sent in as little as one day. But if the same thing was sent by First Class mail, it could take up to three days to get from Kansas City to Virginia.
When you send mail overnight, you pay more than when you send it First Class. The USPS says that sending a letter with a guarantee that it will arrive in two days will cost at least $5 more. Before committing to a guaranteed domestic delivery date between U.S. cities, all post offices take into account things like the size and shape of the package, its weight and characteristics, the need for insurance, how fragile it is, and any other special handling needs. Bring the package to your local post office or another pack-and-ship store to find out about rates and special handling needs.