You can accomplish it at any distance, but also for maximum rate training i personally use 3 yards. The drill is straightforward; you draw from concealment and place two shots to the target since fast as you are able to recognize two sight images. This really is NOT A DOUBLE TAP! A tap that is double two shots with one sight photo and typically causes one shot in the exact middle of the target as well as the other into the top area of this target.
It really is well worth mentioning that many people choose to perform the same drill but just shoot a single round.