Today at 8:00pm EST, there will be 61 seconds in a minute. Why? Because the planet is moving slower than our clocks, reports Bloomberg Business. This leap second has been added 25 times since 1972 — the last time was in 2012.

But what’s good for the planet and timekeeping could pose trouble for stock markets across the globe. That’s because, Bloomberg notes, this is the first time this extra second will be added during trading hours since markets went electronic. To deal with this potential issue, U.S. markets are ending some after-hours trading early.

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For TMX Group, the leap second will be a non-event, says Mathieu Labrèche, manager, Corporate Communications and Public Affairs at TMX Group Limited. “[That’s] because the adjustment will occur at 12:00am Greenwich Mean Time (GMT), which is 8:00pm EST, when our equities and derivatives markets are closed.”

He adds the “clocks will have been adjusted by the time our markets open again on July 2 (since markets will be closed on July 1 for the Canada Day holiday).”

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