The market in California opens at 9:30 a.m., which means that traders need to be in front of their trading desks at 6:30 a.m. The reason behind the 3-hour gap is that some time is required for a conference call, to catch up on the news, and commute to work. You should note that regular trading hours for the stock market in the United States start at 9.:30 a.m. and end at 4 p.m.