The Securities and Exchange Commission issued an order on January 5 granting accelerated approval of NYSE Arca, Inc.’s proposed rule change to its Rule 6.47A, Order Exposure Requirements – OX. The rule change reduces the exposure time during which order entry firms may not execute as principal against orders they represent as agent from three seconds to one second. The SEC believes that market participants should continue to have opportunities to compete for exposed bids and offers within a one-second exposure period, as NYSE Arca reported that a survey of its members indicated that firms could respond to orders within one second.  

http://www.sec.gov/rules/sro/nysearca/2009/34-59194.pdf