Water Level Adjustment: The actual time it takes to raise or lower the water level by 21 feet is around 10-20 minutes, using gravity and requiring about 22 million gallons of water.
MacArthur Lock is smaller (800 ft) than the Poe Lock (1200 ft), but both operate on similar principles.
Direction: It's often quicker if a boat is coming in the opposite direction, as it already sets the water level in your favor.