IB starts executing orders on American stock exchanges at 0400 and doesn't shut it down until 2000, least coast time. But that's not all. Apart from SA - TH 2245 - 2345 and FR 2200 - 0200 system reset times, the system is up around the clock. I sometimes trade E-Minis or Micros with IB and I am often up trading before the 0400 start of the stocks pre-market open. I sometimes trade futures well after the 2000 close of the stock markets, too. IB is far from the perfect brokerage but they do a good job of presenting US traders and investors with good market availability.