19 hours and 39 minutes If you play the Harry Potter movies without stopping, it takes 19 hours and 39 minutes. However, factoring in breaks, the time it takes to change the movies, and any technical difficulties you might have, a full Harry Potter Marathon will take over 20 hours!
Brake pads are not sold in pairs they are sold in sets of 4 pads enough to do 1 axle. Rotors (and drums) are sold per each as it may not be necessary to replace both.
Brake rotors are usually sold individually by parts stores although many manufacturers recommend replacement in pairs. Also, many part suppliers will sell a package or bundle consisting of pads and two rotors which can save you anywhere from a few dollars to a hundred or more, depending on the vehicle.