What is the difference between the cauldrons

Cauldrons differ in the amount of time needed to heat up. This means your cauldron choice will affect how difficult it is to keep the temperature within a certain range. A copper cauldron may be quick to warm up but it also means that temperature will be harder to control. Whether if it is the simple Pewter, Copper or Brass, it will all take the same waiting time to brew until Pottermore makes the necessary changes.