If you want to buy or sell shares at a price that matches or betters the level you specify when the market next opens, you can place a "fill or kill order". Your order with either be "filled" if your broker gets a price matching your requirements or "killed" if the price cannot be matched at the first attempt. You can only place fill and kill orders outside market hours but not between 11.55pm and 3.00am. These orders expire when the market opens on the first business day after the order has been taken. So, if you place a fill or kill order on a Tuesday evening, the order will be filled or killed at the start of the next day's trading.