It's my understanding that an option can be executed well past the close at 4 PM. IB says they will accept orders up till 4:30. Has anyone ever done this, and what is the latest an option can be calling in anywhere for exercise? Since they actually settle on Saturday, someone theoretically could get news late Friday of expiry on some very cheap out of the money options, and call in the stock. It also implies that you don't know for sure that a short option will not be exercised , even if its ootm at the close.