Tonight was the first time for me to place a (smart) market order on a stock after hours (broker = IB, I checked the box "fill before/after regular trading hours"). Normally (with a market order) the system immediately answers that the order is filled. In this case, the system only told that the order was acknowledged by the exchange. And when I tried to cancel it (after I saw it didn't execute) the system hang. When afterwards I placed a limit order, it was filled according to expectations. So can I conclude that one can't use (smart) market orders after hours with IB?