I think it has to do with whether or not you put "Day Order" instead of "Good until Cancelled." Good until Cancelled will push it through ASAP. Day order will buy it at the end or beginning of the day.
As a measure of sheer desperation, I asked my sister for a couple of stock tips. Those stocks are up 650 bucks, while the two I'm hoping will raise (which did finish much higher today) are down on me for 300 bucks.