U.S. Stock Market to Introduce '23 Hours x 5 Days' Trading: Can Clearing and Data Systems Keep Up?

The '23 hours x 5 days' trading is not just about extending hours; data, clearing, and quoting systems must operate 24/7.

Written by: Mike Cahill, Forbes
Compiled by: AididiaoJP, Foresight News

U.S. Stock Market Set to Open '23 Hours x 5 Days', But the Real Question Is Not Whether Trading Hours Are Long Enough

The next phase of the U.S. stock market will be defined by longer trading hours. However, the real question is not about adding a few more hours, but whether the market can maintain institutional-level liquidity when most people are asleep.

On December 6, the U.S. stock market is expected to take its biggest step yet towards continuous trading. Nasdaq, NYSE Arca, 24X National Exchange, and Cboe EDGX are preparing to add an overnight trading session from 9 PM to 4 AM Eastern Time, in addition to the existing pre-market, regular, and after-hours sessions.

This move is in response to global demand and competitive pressure. Investors have long been trading U.S. stocks in alternative trading systems, and the cryptocurrency and prediction markets have led more people to believe that 'around-the-clock trading' should be the norm.

So the question arises: is '23 hours x 5 days' trading merely catering to an existing demand, or will it create a new market out of thin air? The answer is likely both. However, the initial focus may not be on creating new trades, but rather on integrating existing trades into a more cohesive and regulated market structure.

Overnight Demand Has Existed, But Is Highly Concentrated

Overnight trading has been operating through ATS and other venues for many years. Blue Ocean's overnight session runs from Sunday to Thursday, 8 PM to 4 AM Eastern Time; OTC Markets operates from 8 PM to 7:45 AM the next day, offering trading for select securities.

These venues indicate that investors indeed want to trade U.S. stocks during Asian and European hours. The demand comes from several groups: foreign investors wanting to enter during their local trading hours, U.S. retail investors wanting to react to news outside regular hours, and those already accustomed to 24/7 digital markets.

The growth is real, but the scale remains small. In the second quarter, overnight trading accounted for about 1% of U.S. stock trading volume, but the activity volume increased by 358% year-over-year. Foreign investors made up 37% of overnight trading volume, while institutional accounts accounted for only 7%. Trading is also particularly concentrated: in August, an average of only 15 stocks accounted for half of the overnight trading volume.

This set of numbers highlights a key distinction: there is demand for overnight trading, but there is no evidence yet that the entire market has widespread institutional demand for overnight stock trading.

This gap is where exchanges are placing their bets. If the market can provide reliable data, competitive execution, and sufficient liquidity, more institutional funds may follow. If the trading clock is merely extended while the order book remains thin, this new session may at most formalize retail and overseas demand.

Trading Hours Are Not the Answer; Market Quality Is

The principle has always been simple: quality is more important than quantity. The market intends to increase the amount of available data, but it is still unclear who has the capability to consistently provide top-notch and accurate data.

The strongest argument for extending trading hours is convenience. Investors can react to earnings reports, geopolitical events, and fluctuations in overseas markets without waiting for the next U.S. stock market opening. This is useful, but not enough.

The quality of a market ultimately depends on execution quality, not just on how many hours it is open.

Participants in the overnight session are fewer, liquidity providers are fewer, and the order book is thinner. An analysis by BlackRock of actively traded iShares ETFs found that the average overnight bid-ask spread is nearly 10 times wider than during regular hours.

Thus, it is correct for institutional investors to focus on market quality. Wider spreads mean higher trading costs; thin liquidity can amplify price volatility. Quotes may exist, but that does not mean a portfolio can execute meaningful scale at those prices.

The overnight market can still contribute to price discovery. It can absorb new information before regular hours and allow investors to hedge risks when the U.S. stock market is officially closed. However, whether these benefits can be realized depends on whether participation can expand from the current concentration of retail and overseas investors to a broader base.

Before '23 hours x 5 days' trading becomes a truly meaningful institutional trading venue rather than just an extended access window, the market needs deeper liquidity, transparent pricing, and consistent protections.

Extended Trading Hours Require Stress Testing of Infrastructure

Extending trading hours essentially turns 'changes in market hours' into a major test of infrastructure.

Nasdaq's model includes a pause from 8 PM to 9 PM to process and roll over the trading day; overnight trading will be divided into two trading days. This arrangement will affect settlement, financing, reporting, corporate actions, tax processing, customer statements, and market interpretation.

Cboe's plan lays out dependencies clearly: the launch depends on SEC approval, whether DTCC and SIP can support real-time operations, and the timeliness of corporate action data. The NSCC's shift to 24x5 clearing is a necessary step, but it is just the first step required by the industry.

Continuous markets also need continuous information systems. When venues open, quotes and trades must be consolidated; corporate actions must be distributed before they affect trading; regulatory halts must be communicated across venues; and when the last regular session was hours ago, reference prices must be clear.

Order protection is also a similar issue. The SEC proposed in June to repeal Rule 611 of Reg NMS, which prohibits trading through national market system stocks, while also repealing Rule 610(e), which pertains to locked and crossed quotes.

Timing is crucial. During regular hours, companies operate within established frameworks for displaying quotes, routing obligations, and expectations for the national best bid and offer. The overnight market is thinner, more fragmented, and more reliant on each venue's own data.

If the existing trading through framework changes, the industry will need to clarify best execution, quote protection, and venue competition rules. This does not necessarily mean keeping every rule intact, but when liquidity is scarce and investors are more exposed to fragmented pricing, the rules must be clear and discernible.

The market can tolerate a period of low activity. What it cannot tolerate is uncertainty about which price, trading day, corporate action directive, or displayed quote should govern a live order.

'23 Hours x 5 Days' Trading Market Requires a 24/7 Data System

Ultimately, as we move towards a '23 hours x 5 days' trading market, the benchmark is not how novel the 'extended trading hours' are, but whether the market can remain equally clear, resilient, and accountable after dark. Bloomberg's report on the upcoming overnight trading venues captures visible changes; the less visible change is that market data must evolve alongside.

For data providers, brokers, exchanges, and infrastructure companies, this means there can no longer be a clean 'today/tomorrow' boundary. Systems must handle trading days, corporate actions, reference prices, and real-time executable quotes across overlapping periods while maintaining support, monitoring, and maintenance coverage around the clock.

Nasdaq states that this involves years of industry effort among exchanges, regulators, and infrastructure providers. This coordination requires stronger automation, regional support coverage, reliable failover, and clearer processes for deploying changes during market hours.

Two years from now, success cannot be measured solely by the share of trading volume during non-standard hours. More important signals include broader participation, narrower spreads, deeper order books, reduced concentration of a few securities, and consistent, understandable market data across all periods.

If these conditions mature, '23 hours x 5 days' trading could become a new layer of market structure in the U.S. If not, the industry will have merely created a longer trading day without improving the market.