Duration runs from the peak to the recovery of that peak, not to the trough. A decline that bottoms in three weeks and takes fourteen months to recover is a fourteen-month drawdown, and that is the number people actually experience.
It is also the measure that ends careers. A 15% decline is tolerable; a 15% decline lasting two years, during which a passive index rose, produces a slow collapse of conviction that no single day would have caused. Managed futures records regularly show multi-year durations, which is why so few investors capture their long-run returns.
Report the distribution, not just the maximum: the median duration, the longest, and the count of drawdowns exceeding some threshold. See time-to-recovery and flat-time.
Related: time-to-recovery, flat-time, underwater-curve, ulcer-index