The Opening Bell Effect

There is the most trading volume per second during the first and last thirty minutes than during any other point in the day. This means that if you are a fund manager, or large investor, or whale you want to buy/sell during the opening or closing of the market in order to maximize the amount of your inventory that you can accumulate/liquidate.

For example: assume that during 9:30-10:00am you could sell 5 million shares while depressing the market two dollars. During 10:00-10:30 that 5 million would move the stock 10 points. When do you want to sell it? Exactly: during the open. Since you can buy/sell more off the open, price becomes a non-factor. Moving stocks up or down a few percent is a function of how much size people have to accumulate (buy) or distribute (sell) at any given moment.

Since the open and close represent the greatest opportunity for large shareholders to enter and exit quickly, you will always see large orders towards the opening and close of the market.