Regular trading hours are 9:30 a.m. to 4 p.m. ET, but the major U.S. stock exchanges close early on certain days ahead of or just after market holidays. <br> <br>A stock market exchange is, by definition, a marketplace where stocks can be bought and sold for certain hours throughout the day. <br> <br>It functions as an entity that ensures orderly trading and efficient dissemination of price quotes for the companies that list on the exchange.