One of the things that makes these guys' jumpers so quick and lethal is how QUICKLY they get off the ground. These are 3 players that are known to jump quite a bit on their shots (as opposed to guys like Steph + D'angelo), and are lights out shooters.
One of the best ways to improve your rhythm and speed of release is to focus on popping off the ground QUICKLY.
All 3 of these players are always on their toes and consistently get off the ground in a split second. Also, none of these players HANG on their shots.