It is done through software, I basically input I want a 1500 shares (min. size at my firm) bullet and depend on the volume it can take a few seconds. On those summer days it is the same speed as a Direct Plus order.
Today I bought 500 DNA one print off the open at .88 and it started to wiggle, as soon as I saw the offer and market reversing like that I sold, and when the offer got larger I quickly put the order in for the bullet, before the bullet is even confirmed I already filled out the order box for a limit sell, and almost right after I filled out the order box, the bullet is confirmed, boom I sold away, no way you are going to get that filled had you been going natural.
The behind the scene stuff is not important (which is essentially establishing a hedged position with a stock position + married put, giving you ownership to the stock).
Obviously, this is a huge edge when shorting things off the open, and obviously, if you don't use it properly, it won't do you much good . . .