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?
Unless you're trading something extremely liquid, you're going to be paying a multiple dollar spread afterhours.
From IB site: Unlike Limit orders, Market orders are not guaranteed a specific execution price, and we do not accept Smart Routing Market orders when the primary exchange at which an equity trades is closed.
I really wish IB would display the bids & offers of after-hours that are placed by other brokers as well. They go thru on IB, but IB doesn't display them (at least based on the standard quotes package).