Setting time depends on the chocolate and can be anywhere from 15 minutes to an hour.
To get the chocolate to set quickly, you can place the pretzels in the fridge. However, they will need to be kept in the fridge until served as placing them in the fridge increases risk of the chocolate sweating.
Melting chocolate is simply chocolate that does not need to be tempered. Melting chocolate sometimes comes in cubes or wafers.