The stock market is closed on weekends but with Internet trading, you can still go online and place any order on Saturday or Sunday. The buy or sell order will just sit there till Monday morning when it will be executed according to the parameters you set. It is no different than buying stocks after hours.
What risks are there and should you place stock orders during the weekend?
Any online stock order you make on Saturday and Sunday can be changed or deleted before the market opens on Monday so there really is no risk. The only thing that can go wrong is that you forget you placed the order and then some news comes out over the weekend or early Monday morning that would cause you to not want to make it after all. Since you are busy with other things, you might forget to cancel it or don’t get to it in time to cancel it.
As an example, lets say you place an order to buy 1000 shares of any company on Saturday. You make the order because you are online and it is convenient to get it done right then and not have to remember to do it on Monday before the stock market opens. But early Monday morning the futures are way down because of some brand new economic news in Europe that this or that country is on the verge of bankruptcy and all the markets across the world are way down. This is a situation where you might want to sit out and not buy anything, preferring to see what develops throughout the day and week. However, since your order was already placed online during the weekend, you would have to log into your account and cancel it in time before it is executed.
Another example is that really good or bad news about the particular company you want to buy comes out sometime over the weekend or early Monday morning and that news would be enough for you not to not want to buy the stock. Again, you would have to become aware of that news in time to log online to your stock account and delete the order. If you had never made that order over the weekend, you would probably hear the news as you log in to your broker account Monday morning and then be able to decide to hold off and never place it.
Buying and selling stocks on the weekend is really only done for convenience. If you are thinking about a stock, you can place any order right then and not have to remember to do it on Monday. Stock investors research stocks on their days off and if they make their decision right then, it is just more convenient to go online and place the order at that time and get it over with. Monday mornings are busy for most people and remembering to buy or sell a stock before the market opens is something that might easily be forgotten.
The only drawback of placing stock orders on the weekend is that you have to remember you did it. That way, if your opinion changes, you will hopefully have time to get online and cancel the order.