3-5 minutes is pretty short. A minute or so talking about the history of playing cards (They are quite old, used for fortune telling before Tarot was invented, which was for a specific game and/or preaching), the difference between card manipulation and card tricks, some notable card magicians such as Hofsinzer, Houdini, Cardini, Malini, Vernon, Miller, Curry - the Out Of This World story is a good one. Then contemporary card magicians like Richard Turner, Jason England, Daniel Madison, the Buck Twins, and of course, David Blaine. Honestly, I'm not even sure you'd have time to do a trick in this speech without running over significantly.