Stock buying and selling on Wall Street ahead of the open has surged over the past three years, a sign that investors are extending the traditional trading day as they assess company news in real time.

In 2019, about 384 million shares changed hands every day, outside of the US standard 9 a.m. to 4 p.m. opening hours. Such transactions are typically conducted on electronic markets, which are often owned by the largest exchanges in the United States and operate on both sides of the main trading hours.

By 2021, that number has risen to 694 million, according to the New York Stock Exchange. Exchange research this week showed that while out-of-hours trades fell in the first quarter of 2022, they still averaged 682 million trades per day.

Stefanos Bazinas, an executive strategist at the New York Stock Exchange, said the “spike” in after-hours volumes was largely due to a rapid increase in pre-market volumes. Three years ago, so-called “pre-market” trades averaged 62 million, or about 16 percent of all out-of-hours trades, but last year it hit 265 million, or 38 percent of the total.

Some have attributed the uptick in trading outside Wall Street’s regular trading hours to investors’ quicker reaction to company earnings releases, which flank the main trading session as the information is market-sensitive.

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“U.S. stocks, especially global tech brands, are very popular overseas, where people are reacting to news and global developments in real-time during their waking hours,” said Joe Gorenski, chief executive of Rosenblatt Securities. Joe Gawronski) said.

The use of forums such as Reddit by retail investors to support the growth of so-called meme stocks such as GameStop is also the “driving force” behind out-of-hours trading, Bazinos wrote. In March 2022, small trades accounted for 8% of premarket trading, compared to 2% in January 2019.

The NYSE’s findings add to a growing debate in the U.S. over the length of the trading day — concerns that more out-of-hours activity, especially during the European morning, could exacerbate troubled days with low trading volumes in the mid-America, exacerbate price volatility.

Gawronski said many retail investors have become accustomed to using the app to trade when they want, encouraged by 24/7 access to cryptocurrency trading.

Bermuda-based 24 Exchange filed with U.S. regulators in October to launch the first all-day U.S. stock exchange with a trading volume of 1,000 shares. In March, Robinhood, one of the most popular U.S. brokerages, extended its hours by four hours to bring it in line with rivals like Schwab and Fidelity.

However, even with the mushrooming of after-hours trading, the US market sees an average of 12.8 billion shares traded during normal hours a day. For now, most of the activity is still concentrated in the last half hour of the day.