If you trade the US session, the best time is from 8am - 12 noon EST. Sometimes I'd stretch one hour to about 1PM. As others mentioned, that last 30 minutes before the old pit closing time (2 - 2:30PM) can be volatile, but I can't find tradable setups at that time using my method. Your mileage may vary.
Also check your broker for margin requirement if you use very high leverage. My broker sets 9am to 3:45pm as intraday. So any trade beyond this time will be considered overnight and require a higher margin.