Trading volumes and prices can be quite volatile during the opening period, which runs from 9:30 a.m.2 to 10:30 a.m. Eastern Time. This is because the market factors in all the events and news releases since the previous closing bell, leading to price fluctuations.2 Many professional day traders start trading as early as 8:30 a.m.123 (premarket) and begin tapering off around 10:30 a.m. As the day progresses, trading volumes tend to decrease, and the market becomes less volatile. 2