We will run Barracks Boost Events from time to time and during the event, you can boost the summoning speed of all your barracks by 3x at a low cost! Keep an eye on the System Announcement and boost responsibly when time comes

The boost effect doesn't apply to the speed-up items or Instant Complete. The Speed-ups and Instant Complete work only on the original summoning time.
Once the boost is activated, the countdown will continue regardless whether there are troops in Barracks or not.