Trading on the New York Stock Exchange normally begins each weekday at 9:30 a.m. Eastern time and concludes at 4 p.m. Eastern time, according to the official NYSE website. The NYSE has a shortened trading day or is closed entirely in observance of certain holidays.
The NYSE was only open from 10 a.m. until 3:30 p.m. until 1974, according to the Los Angeles Times. As volume grew, the exchange began closing at 4:00 p.m. in 1974 and then began opening at 9:30 a.m. in 1985.
Trading can take place outside the NYSE's official opening hours, explains Investopedia. After-hours trading allows investors to react to breaking news outside of the trading day, but after-hours trades also may be executed at less advantageous prices due to a lack of liquidity.