Round here, there's a place called "Fleet Feet" that will custom fit your shoes and shape/trim insoles on the spot.
"Fleet Feet Sports is a group of 67 stores specializing in footwear and apparel for North America’s runners, joggers, and walkers. Each store is a locally owned and operated franchise of Fleet Feet, Inc. The people of Fleet Feet are athletes who take the time to understand their customers’ footwear and apparel needs. While each store is centrally focused on running and walking, the unique sports and fitness needs of its local market are represented."
http://www.fleetfeet.com/
16 hours is a long time to be on your feet. You'll do yourself a favor if you can find some comfortable shoes. Off the rack sneakers are not going to cut it if they are not a good fit for your feet.
You'll spend a little more at a specialty store, but chances are it will be worth it. If the pain persists no matter what, go see a podiatrist (foot doc).
Hope that helps,
Andrew Lopez, RN
http://www.nursinga2z.com