What is letdown, and how long does it last?

Milk ejection reflex. As the baby latches on and suckes, the body releases a hormone called oxytocin. This hormone signals the muscles in the ducts to contract and move the milk out of the breast to the baby. Moms may experience tingling at the onset that may last about a minute. Let down will last as long as you nurse.
Milk moving . Let down is when the milk in the breast glands moves into the ductwork for expulsion when the baby sucks. The actual sensation usually lasts for 30-180 seconds but can last longer.