The power hour is the last hour of regular trading on U.S. stock exchanges, usually from 3 p.m. to 4 p.m. Eastern Time. This period is known for heightened trading activity, as institutional investors and traders execute end-of-day orders, rebalance portfolios, and react to late-breaking news. Increased volume and volatility during this time can lead to sharp price movements, making it a key focus for short-term traders and market analysts.