I bought a 24 cup cupcake pan from a restaurant supply store because I am baking cupcakes for my daughter's wedding. The cups are regular size, just in one big pan. Should I place the pan on the middle rack, as usual, and do they need to bake longer?
Yes and Maybe. You should definitely place the pan 'centered on the center rack' of a well pre-heated oven. The heat should be absorbed evenly and allow all of the cupcakes to bake at the same pace. (If your oven has 'hot spots' you may wish to rotate the pan once, 180°, about half way through the expected cooking time).
As for how long to bake them, do not let time @ temp be your guide to 'done'. As with any cake, use the toothpick test (stick a toothpick into the center of a cupcake and pull it out, if it is clean, they are done.) You should start testing this way at the 'expected' baking time.