I don't know about you but I don't take much longer than a second or two to formulate things I'm going to say to people.
Yet actually saying
them (which is either the brain>mouth or the mouth>ears part) does take several seconds, unless it's a simple "Fire!". And it's not as if Kirk or Picard chooses to use the shortest possible phrasing, either. Which both extends the output time, and makes it more difficult for the listener to decipher the input.
That's hardly the most damning fault in the practice, though. The worst time-hog is the skipper's need to micromanage the use of weapons. In most situations, he or she has a dedicated weapons officer available to control the weapons systems, and he or she in turn supposedly has underlings next to the actual weapons. The skipper's role thus should really be just "take down all of them" or "take out their propulsion", not "prepare forward photon torpedoes - target their engines - on my mark, fire - fire!".