How long mail takes is going to depend on many factors along the way. Many factors, indeed, though with regard to how long does priority mail take, the answer is, not long. In fact, the United States Postal Service says your package or envelope will arrive within two days.
Both the 2009 IRC and the DCA6-09 allow #2 southern pine 2x10s to span 13 feet 1 inch at 24 inches on-center at a design load of 50 psf. That means these joists can span the 12-foot depth of the deck, and the beam can be located at the perimeter. Nine joists will be needed for the 16-foot width.
When I'm unsure of the ability of a 2x12 rim joist on a deck with 2x8 or 2x10 framing to support the load from the stairs, I provide independent support by installing a single-ply header directly beneath the rim joist. The header is screwed to 4x4 posts and bears on 2x4s that are screwed to the 4x4s below the header.