I am using IB and it displays ISE bids and asks preopen but it doesn't allow preopen trading. I don't understand why quotes are being shown if the exchange isn't open yet. This causes problems if I try to use Smart order routing preopen. If I try to buy a stock at the asking price with the exchange set as Smart, the ISE ask is often the best but the order gets routed to Island since ISE isn't open. For those who trade outside of regular trading hours what exchange do you think is best?