The North-American stock market opens at 9:30AM ET and closes at 4:00PM ET. Any trade made when markets are closed will be processed the next business day. This is only true for stocks, bonds and mutual funds. Futures trade at different times.
Markets are CLOSED for these Federal Holidays in the U.S.: New Year's Day, Martin Luther King, Jr. Day, Presidents' Day, Memorial Day, Independence Day, Labor Day, Thanksgiving Day, and Christmas Day (observed). On the day following Thanksgiving and frequently the day before Christmas, the market will close at 1:00 pm ET.