The Hong Kong stock market is open 9:30am - 12:00pm and 1:00pm - 4:10pm.
The Pre-opening Trading Session starts at 9:00am.
The U.S. stock markets are open 9.30am - 4:00pm EST.
This is 9.30pm to 4:00am (daylight savings time) and 10.30pm to 5:00am (standard time).
You can start placing orders for the next trading day, 30 minutes after market close.