For decades, 4:00pm has given compliance teams a clean dividing line. Pre-clearance approvals lapse at the close, blackout periods start or finish, restricted-list updates come into force, and employees know exactly when an approval stops being valid. That certainty is about to disappear.

According to StarCompliance, from 6 December 2026, Nasdaq and NYSE plan to run a trading schedule from Sunday at 9:00pm ET through to Friday at 8:00pm, broken only by a planned one-hour maintenance window each evening. Technically the market will still close, but the pause is closer to a quick nap than a full night’s rest.

Across the Atlantic, the London Stock Exchange has signalled that LSE24 is expected to launch in the first half of 2027. The question for compliance functions is simple but uncomfortable: what does “market close” actually mean when equities can trade for 23 hours a day?

The SEC’s roundtable on 17 September examined the wider consequences of round-the-clock trading, covering overnight surveillance, clearing and settlement, investor protection, cybersecurity, staffing, systems resilience and market-data continuity.

Commissioner Hester Peirce also flagged concerns around supervision, thinner overnight order books, wider spreads and the practical difficulty of handling problems at 3:00am. For compliance teams, this is not merely an extra session bolted onto the day. It undermines assumptions baked into policies and controls designed around a clearly bounded trading day.

Overnight activity is still a small slice of the US equity market, but it is growing fast. 6m shares, with more than 4,200 NMS stocks trading overnight on a typical day.

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