Not sure how many people this will affect, but the CBOE has a new settlement procedure for the VIX. The VIX settlement price is based on the opening price of certain SPX options. In the past retail customers could participate in this SPX opening process, which gave retail customers a nice edge. Now in order to participate in the SPX opening (for the series that determine the VIX price) orders, cancels or modifications of these SPX options will not be accepted after 820am ct. If you want to place an order after 820 for the opening, it will have to be marked with the designation "SLOO" Note that most brokers are not aware of this. So be aware that if you have regular order in before 820 ct. in the SPX for one of these series (tomorrow it would be the Nov monthly expiration) you wont be able to cancel it after 820 until after the opening.