This has never happened but I am curious. Suppose 4:15PM EST, on the third Friday of the month (options expiration day) arrives, and all the ES (s&p 500 emini) options expire. Suppose one has a short option ITM. Obviously, this option will be assigned. Is the assignment and reception of the underlying futures completed by 6:00 PM EST when the s&p 500 emini market opens? If so, then I should be able to close them out at that time--correct? Seems to me that to avoid any volatility, it is best to close out the assigned futures at the open (6:00PM EST) rather than wait until morning. Comments appreciated. FYI, I typically cover ITM options or just close them out before 4:15PM on expiration Friday.
In practice your broker will know sometime after 8pm on Friday, and it will post to your account before Sunday's 6pm open. Squeezing an extra tic or two on a short option over the weekend is pure gambling unless you're covered and know for sure you're getting assigned. ABC - Always be closing!