I am a newbie and have what may be a fairly basic question. Suppose the stock of a large heavily traded company (e.g. GE, CAT, AAPL, etc.) closes at 4 pm on Monday at a price of $20.00 per share. Suppose that I place an after-hours/extended hours limit order to buy at $20.50. Then suppose the stock opens at $21.00 the next morning at 9 a.m. What is the probability that my buy order will be executed within +- $0.10 of my limit order price overnight, sometime between the close and the open of the regular market? Put a different way: what percentage of such orders will remain unexecuted the next morning? Is the outcome fairly predictable, or so variable from stock to stock and ECN to ECN that the question itself is silly?
If it closes at $20 and there isn't any news out that would affect its price, and you put in an extended session order to buy at $20.50, it will probably get filled immediately. Some stocks trade actively after-hours, some don't and have very high asks and very low bids and 20.50 might not be high enough to hit the ask. If it doesn't get filled by 8PM, the order will be canceled. The order might be placed again during pre-market hours the next day if you specified good-until-canceled and if your broker supports GTC extended-hours orders. Not many do. The question then becomes, when do they submit the order? Some will do so at 4:15AM. Some at 7AM. Most at 8AM. As to +- .10, a limit order to buy won't be filled at a price higher than you specified, although there have been reports here about mistakenly good fills being adjusted to higher prices.