I just finished reading Flash Boys by Michael Lewis, it was an incredibly enlightening read. To answer your questions:<p>1) I think it&#x27;s 350mcs across the board except in the case of firms which conduct suspect activity (canceling orders frequently for example). Adding the delay institutes a level playing field across anyone trading on the exchange. The basis of HFT is leveraging faster connection speeds to gain insight into other&#x27;s trading strategies and exploiting those strategies, all before the other firm&#x27;s trade reach the exchange. This is a HIGHLY simplistic explanation dealing with one form of arbitrage and given for brevity on the subject.<p>2) EDIT: the other guy explained this better!<p>To your point about 350mcs being absurd to argue over, HFT firms manage regular trading speeds in NANOSECONDS. Look at 350mcs in those terms (350,000 nanoseconds) and it&#x27;s not such a small number anymore.