Notice of Designation of a Longer Period for Commission Action on Proceedings To Determine Whether To Approve or Disapprove a Proposed Rule Change, as Modified by Amendment No. 1, To Amend Rules 5.37, 5.38, and 5.73 Related to Auction Notification Messages and Index Combo Orders in SPX in the Automated Improvement Mechanism, Complex Automated Improvement Mechanism, and FLEX Automated Improvement Mechanism