[pclmulqdq]

As far as I know, you're correct that this exact trade probably doesn't happen on the US exchanges - day orders do have a matching phase before market open, so it may be advantageous to slide in right afterward, but you likely wouldn't do it without knowledge of the state of the opening auction.

However, sending things just a hair early for scheduled events to catch an exact time is a pretty well-known trick at this point. I remember complaining to the exchange that their clocks weren't precise enough for this to be reliable.