when i put on an order to trade SPX spread (whatever spread with 2 or more legs), the turn around time could be as much as one minute. Quite often, i thought i may have to increase my bid price for buy order (or decrease ask price for sell). I adjusted the price, but a few tens of seconds later the order was executed at my previous price. this does not happen with RUT spread, which orders are mostly routed to ISE. does anybody know the mechanic behind the execution of SPX spread?? how long should i wait to see if my order got executed before adjusting the price????