Dallas, this is from Scottrade..............
For example, if you make a sell on Monday the 1st, you could use this money to make a purchase prior to the settlement date, however, if you sell and you use the money to make a purchase before Thursday 4th, you cannot sell those stocks until the original sell from the 1st settles. If you do, you will then need to bring in money to pay for the purchase. If you purchase on Thursday the 4th, you may place a sell at anytime you wish, since these are settled funds