Five minutes is the gold standard for box breathing. This is the session length used in Navy SEAL training, recommended in clinical protocols, and backed by the most research. At approximately 19 cycles, your body completes a thorough autonomic reset — heart rate drops, blood pressure normalizes, and cortisol begins actively clearing from your bloodstream.
The difference between 3 and 5 minutes is the depth of the reset. At 3 minutes, you've initiated the shift. At 5 minutes, you've completed it. Many practitioners describe the 4th and 5th minutes as where box breathing "clicks" — the breathing becomes effortless and a distinct sense of calm alertness emerges.