I have been using stop orders for covering short option positions using the 'best' category, which appears to be creating a synthetic stop until execution. This has been working reasonably well for both long and short positions on the qqq's, with most orders ending up going through island. However, last week I had a situation where the order for a long did not get transmitted to an exchange for several minutes while the price continued to move solidly beyond the stop price. Once transmitted, the order was filled rapidly, but I could not understand why the order just seemed to hang for several minutes before being sent to an exchange. I was reluctant to try and cancel out the stop and do the order by hand, thinking that I might easily end up making things worse. I was wondering why this happens and how to avoid it in the future.