Trading hours are the specific time windows during which a stock exchange accepts and processes buy and sell orders. Each exchange sets its own regular trading hours based on its local time zone. For example, the NYSE and NASDAQ operate from 9:30 AM to 4:00 PM Eastern Time on weekdays. Outside of these hours, orders are either rejected or held until the next session opens. Regular trading hours offer the highest liquidity, tightest spreads, and most reliable price discovery. Most exchanges also define extended trading periods (pre-market and after-hours) with different rules and lower participation. Understanding the exact trading hours for each exchange you trade on is foundational for managing orders, avoiding rejected trades, and planning your trading schedule around peak activity periods.