Howdy
OK, here is the deal. With a single action revolver, like the classic Colt Single Action Army, or any single action with the same style mechanism, you will get four clicks when you cock the hammer.
The first click happens when the hammer is drawn back about 1/8" and the sear falls into the so called 'safety cock notch' on the hammer. The second click happens at half cock, when the sear falls into the half cock notch on the hammer. This is the loading position for this style revolver, the bolt has been withdrawn at this point and the cylinder is free to spin for loading and unloading. The third click is the bolt popping up against the surface of the cylinder, and the fourth click is the hammer going to full cock. If you cock the hammer very slowly, you may hear five clicks with a SAA or similar single action revolver. If the revolver is not perfectly timed, and most are not, the hammer will go to full cock a teeny bit before the bolt pops into the locking slot on the cylinder. But for all intents and purposes, a Colt Single Action Army and its replicas have four clicks when cocking the hammer.
Modern double action revolvers have a very different mechanism. Generally speaking, when cocking the hammer on a modern double action you will hear a soft click as the bolt pops up against the cylinder, then a louder click as the hammer goes to full cock. There are no 'safety cock' or half cock notches on the hammer of a modern double action revolver. Again, if the revolver is not perfectly timed, you may hear the hammer go to full cock a teeny bit before the bolt pops into the locking slot on the cylinder, but you would have to put some drag on the cylinder and listen very closely to hear two separate clicks at the end of the cycle.