Rethinking overnight markets: The market data impact of 24×5 trading

The move toward 24×5 trading in US equities is often framed as an extension of market hours, a definition that oversimplifies the impact. More fundamentally, it challenges one of the most basic assumptions underpinning how markets, systems and data operate today – that there is a clear overnight pause.

As US exchanges move toward near-continuous trading, the concept of “overnight” is beginning to lose its traditional meaning. Markets may pause briefly, but they no longer fully switch off. Recent announcements, including plans for LSE 24, point to broader global demand for extended market access, including in UK equities. This raises practical questions for technology, data and operations teams about how systems behave, how data is processed, and how reliably decisions can be made when quiet periods become shorter and less predictable.

Much of the discussion around extended hours has focused on how trading will work, when changes will go live and which venues are involved. Less attention has been paid to what this shift means for market data and the operating models that sit beneath trading itself. That perspective matters because decisions about data workflows, systems and support models are not made by traders alone. They sit with operators and senior decision‑makers whose assumptions have historically relied on overnight inactivity.

For many market data professionals, the most immediate concern is not trading opportunity but operational impact.

Existing legacy systems and processes, many of which have operated reliably for decades, are built around well understood market rhythms. End-of-day processing, overnight maintenance windows, reconciliation runs and reference data updates all assumed a prolonged period of inactivity. Near-continuous trading compresses those assumptions.

As exchanges extend trading into what was previously the overnight window, firms may need to revisit how they define trading days, schedule processing jobs and manage support coverage, often within technology environments that were designed for a clear overnight pause. Even modest changes to timing can ripple across downstream analytics, reporting workflows, and risk controls. In practice, many of these dependencies only become visible when something breaks, for example when a reference update no longer aligns cleanly with a trading boundary or a downstream process assumes a quiet period that no longer exists.

None of this implies an abrupt break from the current model. Change will be phased and many details are still being finalised. But it does mean that firms will increasingly need to operate in an environment where overnight is quieter, rather than inactive.

For practitioners who work with market data day-to-day, the earliest signals of change are unlikely to be dramatic spikes in volume. Instead, they will appear as differences in what is visible and when.

As extended trading is introduced, data coverage will evolve incrementally. Data consumers will need to adjust to clearer distinctions between venue-level activity, consolidated market views, and which sources should be treated as authoritative for different use cases.

In practice, this means new expectations around timing and composition of familiar datasets, including summary statistics, end-of-day measures and the treatment of corporate events. For a period, consolidated and non‑consolidated views of the market are likely to coexist more visibly than they have in the past.

If the operational implications are real, why is the market moving this way?

The answer lies partly in how and where US equities are already being used, but also in broader global demand for access to major equity markets across a wide range of local trading hours. Investors, brokers and platforms increasingly operate across time zones. Asia‑based participants in particular have long engaged with US markets outside core exchange hours, often relying on fragmented or indirect signals via derivatives, indicative pricing, off‑exchange activity and secondary markets. At the same time, growing global demand for widely traded US stocks and leveraged instruments, together with the rise of retail investing and advances in trading technology are increasing both the appetite for, and feasibility of, more extended market access.

Extended exchange trading begins to address that gap. It enables participants to engage with US equities during local business hours, supports new participation models such as retail brokers seeking alternative pricing sources, and brings pricing, reference data and corporate actions closer to underlying events. In this context, 24×5 trading is not simply about convenience, it is about aligning market access and data availability with a global, always-on information environment.

One of the more subtle shifts introduced by extended hours is how overnight risk is perceived. While overnight periods are likely to remain lower in absolute trading volume, they are increasingly high‑sensitivity windows. Corporate announcements, macroeconomic releases and geopolitical developments often emerge during these hours, meaning even a small number of trades can carry disproportionate importance for prices, benchmarks and early‑session positioning.

This dynamic is not entirely new, and overnight trading in US equities has existed for several years through Alternative Trading Systems such as Blue Ocean ATS (which operates between 20:00 and 04:00 ET). Both liquidity and the number of instruments traded have been steadily increasing over time, particularly in widely followed single stocks and ETFs. Liquidity can also rise during any overnight geopolitical or macro events, which may prompt more traditional market participants to seek greater visibility into overnight market activity. LSEG already distributes pricing and order book data from Blue Ocean ATS through its real‑time services, giving clients access to overnight trading dynamics today.

This growth in overnight activity is occurring against a backdrop of rising demand for market data more broadly. Peak message rates on LSEG Real-Time have nearly doubled in recent years, reaching 27 million messages per second in May 2026. Driven by a combination of geopolitical events, heightened market volatility and continually improving hardware capabilities that support greater trading activity, this trend highlights the increasing demands being placed on market data infrastructure. As trading activity extends across more hours, firms may need to process and analyse growing volumes of data across an increasingly continuous trading lifecycle.

What is changing is not the existence of overnight trading, but its role within the broader market structure. Exchange‑led overnight sessions may migrate activity into regulated environments and, over time, introduce greater consistency across venues. In parallel, as automated and AI‑driven trading strategies become more prevalent, they may become less constrained by traditional trading sessions and time zones, while still needing to adapt to how markets behave during core trading hours compared with overnight sessions. Supporting those increasingly continuous and automated market models will require infrastructure to evolve in parallel.

Major US exchanges have proposed extending trading to operate on a 24×5 basis, expanding the current 04:00 – 20:00 ET trading day to a new window of approximately 21:00 – 20:00 ET, with a one-hour daily maintenance period.

Regulatory applications from Nasdaq, Cboe EDGX, NYSE Arca and 24X Exchange and a more recent fifth from MEMX Exchange alongside proposed changes from both Securities Information Processors (SIPs), point to a coordinated shift rather than isolated experimentation. Much of this coordination is centred on how core market functions such as consolidation, National Best Bid and Offer (NBBO) visibility and reporting conventions should operate in a near-continuous trading environment.

At the same time, coordination may not always be uniform. In some cases, individual venues may seek to move at different speeds, only four, possibly five, of the eighteen US equity exchanges plan to trade overnight initially. As a result, while SIPs remain a critical dependency for fully consolidated overnight trading, elements of the transition are likely to unfold in phases as infrastructure readiness, industry alignment and regulatory approvals converge.

Near-continuous trading challenges long-standing concepts such as end-of-day and overnight processing.

Over time, extended exchange activity is expected to influence processing patterns across real-time feeds, historical time series, tick data and reference services. It may also prompt changes to end-of-day processing conventions and embargo periods across the industry, reflecting the challenge of applying traditional market-day definitions in a more continuous trading environment. Many of the practical details, including session boundaries, cut‑offs, and industry conventions, are still in the process of being defined, reflecting how market structure, regulation and infrastructure are evolving together.

What matters most is recognising the shift in operating assumptions. Firms that understand where workflows rely on quiet periods will be better placed to adapt as conventions evolve.

Consistent access to real-time, historical and reference datasets, together with transparency around how activity is consolidated and classified across venues will become increasingly important as market structures evolve. LSEG helps clients navigate this complexity through harmonisation across SIP, exchange and ATS data, managed services, and clear delineation between consolidated and non‑consolidated activity as markets transition.

Although the current regulatory applications are focused on US equity exchanges, longer and more continuous trading sessions are being explored by exchanges around the world. Market structure developments adopted in the US have historically influenced other major venues, but they are also part of a broader global trend toward greater market accessibility and extended trading hours.

The move toward 24×5 trading represents a broader structural evolution. It is not just about trading for longer but about adapting to a world where markets pause less and data flows more continuously. Signs of this shift are already emerging across global markets, including through plans for LSE 24 in the UK. Elsewhere, KRX in Korea is seeking to extend trading hours this year and may also move to 24 hours next year. German exchanges as of last year now offer retail trading until 22:00.

As overnight no longer means inactive, resilience, consistency and clear data strategies become even more important.