US Stocks Set for “23x5” Trading: Can Clearing and Data Systems Keep Up?

The U.S. Stock Market Is Set to Trade “23 Hours x 5 Days,” but the Real Question Isn’t Whether Trading Hours Are Long Enough

The next phase of the U.S. equity market will be defined by longer trading hours. But the real question isn't "how many extra hours," but whether the market can maintain institutional-grade liquidity when most people are asleep.

On Dec. 6, the U.S. stock market is expected to take its biggest step yet toward continuous trading. Nasdaq, NYSE Arca, 24X National Exchange, and Cboe EDGX are preparing to add an overnight session from 9 p.m. to 4 a.m. Eastern Time, on top of existing pre-market, regular, and post-market hours.

This move responds to global demand and is driven by competition. Investors have long been buying and selling U.S. equities through alternative trading systems, and the crypto and prediction markets have led more and more people to view "around-the-clock trading" as the default norm.

So here's the question: Is “23 hours x 5 days” trading capturing demand that already exists elsewhere, or inventing an entirely new market? The answer is likely both. But the first phase may focus less on creating new trades and more on moving existing ones into a more integrated, regulated market structure.

Overnight Demand Exists, but It’s Highly Concentrated

Overnight trading has already run for years through ATSs and other venues. Blue Ocean’s overnight session runs from Sunday to Thursday, 8 p.m. to 4 a.m. ET; OTC Markets offers trading in select securities from 8 p.m. to 7:45 a.m. the following day.

These venues demonstrate that investors do want to trade U.S. equities during Asian and European sessions. Demand comes from several groups: foreign investors looking to enter during their local trading hours, U.S. retail traders wanting to react to news outside regular hours, and those already accustomed to around-the-clock digital markets.

Growth is real, but scale remains modest. In Q2, overnight trading accounted for roughly 1% of U.S. equity volume, though activity surged 358% year over year. Foreign investors made up 37% of overnight volume, while institutional accounts accounted for just 7%. Trading was also highly concentrated: in August, an average of just 15 stocks accounted for half of all overnight volume.

These figures highlight a key distinction: there is demand for overnight trading, but no evidence yet of broad institutional demand across the entire market for overnight equity trading.

This gap is where exchanges are placing their bets. If the market can deliver reliable data, competitive execution, and sufficient liquidity, more institutional capital could follow. If it merely extends the trading clock while leaving order books painfully thin, the new session will at best simply formalize retail and overseas demand.

Longer Hours Aren’t the Answer; Market Quality Is

The principle has always been straightforward: quality matters more than quantity. The market plans to increase available data volume, but who can consistently provide top-tier, accurate data remains unclear.

The most compelling reason to extend trading hours is, of course, convenience. Investors won’t need to wait for the next U.S. equity open to react to earnings, geopolitical events, or overseas market volatility. That’s useful, but not enough.

Ultimately, a market’s caliber depends on execution quality, not just how many hours it’s open.

The overnight session features fewer participants, fewer liquidity providers, and thinner order books. An analysis by BlackRock of actively traded iShares ETFs found that overnight bid-ask spreads are, on average, nearly 10 times wider than during regular hours.

Thus, it makes sense for institutional investors to prioritize market quality. Wider spreads mean higher transaction costs; thin liquidity amplifies price volatility. Quotes may exist, but they don’t guarantee a portfolio can execute meaningful size near those prices.

The overnight market can still contribute to price discovery. It can absorb new information before regular hours and allow investors to hedge risk while U.S. equities are officially closed. But whether these benefits materialize depends on expanding participation beyond its current concentration in retail and overseas players.

Before “23 hours x 5 days” trading becomes a genuinely meaningful venue for institutional activity rather than just an extended access window, the market will require deeper liquidity, transparent pricing, and consistent safeguards.

Extending Hours Puts Infrastructure Under Stress First

Extending trading hours essentially turns “changing market sessions” into a major infrastructure stress test.

Nasdaq’s model includes a pause from 8 p.m. to 9 p.m. to process and roll trading days; overnight trades will be allocated across two different settlement days. This arrangement impacts clearing, financing, reporting, corporate actions, tax treatment, customer statements, and quote interpretation.

Cboe’s plan lays out dependencies clearly: going live hinges on SEC approval, whether DTCC and the SIP can support real-time processing, and the timeliness of corporate action data. NSCC’s shift to 24x5 clearing is a necessary step, but it’s only the industry’s first step.

Continuous markets also require continuous information systems. When various venues go live, quotes and trades must be consolidated; corporate actions must be distributed before impacting trading; regulatory halts must propagate across venues; and reference prices must remain clear when the last regular session closed hours ago.

Order protection presents the same challenge. In June, the SEC proposed repealing Rule 611 of Reg NMS, which removes the anti-trade-through provisions for national market system stocks, alongside Rule 610(e), which covers locked and crossed quotes.

Timing is critical. During regular hours, companies operate within established frameworks for displayed quotes, routing obligations, and expectations surrounding the National Best Bid and Offer (NBBO). The overnight market is thinner, more fragmented, and relies more heavily on venue-specific data.

If the existing trade-through framework changes, the industry will need clear rules on best execution, quote protection, and venue competition. Not every rule needs to be preserved intact, but when liquidity is scarce and investors are more exposed to fragmented pricing, the rules must be distinct and unambiguous.

The market can tolerate low activity for a period. What it cannot endure is uncertainty over which price, settlement day, corporate action directive, or displayed quote actually constrains a live order.

A “23 Hours x 5 Days” Market Requires a 24/7 Data Architecture

At its core, the benchmark for moving toward a “23 hours x 5 days” trading market isn’t how novel “longer hours” sound, but whether the market remains equally clear, resilient, and accountable after dark. Bloomberg’s coverage of the upcoming overnight exchange captures visible changes; the less visible one is that market data must evolve alongside them.

For data vendors, brokers, exchanges, and infrastructure companies, this means the clean “today/tomorrow” boundary is gone. Systems must process trading days, corporate actions, reference prices, and real-time executable quotes across overlapping sessions while maintaining round-the-clock support, monitoring, and maintenance coverage.

Nasdaq states this is a multi-year industry effort involving exchanges, regulators, and infrastructure providers. Such coordination requires stronger automation, regional support coverage, reliable failover, and clearer processes for deploying changes during market operations.

Two years from now, success shouldn’t be measured solely by the share of volume in non-standard sessions. More telling signals will be broader participation, tighter spreads, deeper order books, declining concentration in a handful of securities, and unified, comprehensible market data across every session.

If these conditions mature, “23 hours x 5 days” trading could become a new layer of the U.S. market structure. Without them, the industry will have simply built a longer trading day without building a better market.

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