Those guys put their orders in the instant the mar
Post# of 85484
Back when I first learned how to trade, 20+ years ago, the platform we were using allowed us to route orders to whatever MM we wanted, regardless of price. So even if it was the middle of the trading day, we could hit any MM who was displayed anywhere on the quote.
I'm not sure if those kind of platforms still exist for retail traders, but it's important to remember that there are lots of platforms we don't have access to with the large commercial brokerages.
As far as the legality, I think it's legal to a point, but I doubt there are many investigations into the practice.