Also, try sending an discretionary order to a NYSE floorbroker. They have advantages on the floor and can get you filled even after cutoff times. Please note they need to accept the order on their tablet, though, so that takes around 30 seconds on normal days and more on busy days.
Many NYSE...
Provided you can set up a synthetic stop that is held at your server I would suggest you send the order to an SOR once fired.
Another option would be to send it to IEX Router. They have a logic to eliminate time delays in routing.
If you have to send it natively to an exchange, you can submit...