The final minutes of the trading day are crucial to traders trying to gauge the cost of a trade versus the closing sale, which is why a lot of action takes place just before the close, trader Peter Costa said Thursday.
According to The Wall Street Journal, index funds and computer models are pushing trades toward the end of the day. Trades have increased nearly 5 percent since 2007, with more than one in six trades in S&P stocks taking place in the last 30 minutes, the paper said.
"If you look at volumes right before the close and after the close, I think it's a lot more than what that report says," Costa, president of Empire Executions, said in an interview with CNBC's "Closing Bell."
"I think it could almost border on 20 percent of the trading volume of the day is done in that last minute. … It becomes very, very important. Our firm has built a whole business around it."
Ben Willis, senior floor broker with Princeton Securities Group, said it began with mutual fund traders trying to beat the volume weighted average price, and that has continued into ETF and index trading.
However, he warned that while this could present an opportunity for individuals, it is one for "very sophisticated individuals. This is not a children's game."
One thing that has been lost in this move towards the close is brokers' innate ability to read markets going "further and further away," Costa added. "It changes the rhythm of the day."