U.S. stock trading hours adjusted as the United States enters Daylight Saving Time.

On Sunday, March 9, Beijing time, the United States officially enters Daylight Saving Time, which means that starting from March 10, the trading hours of the US stock market will move one hour earlier. Specifically, pre-market trading hours will change to 4:00 PM to 9:30 PM Beijing time, regular trading hours from 9:30 PM to 4:00 AM the following day, and post-market trading hours from 4:00 AM to 8:00 AM. This change is due to the Daylight Saving Time adjustment plan implemented by the US since 2007.

Background and Evolution of Daylight Saving Time

Daylight Saving Time (DST), also known as Daylight Savings Time, is a system where time is adjusted to save energy. Typically, in summer, when dawn comes early, the clocks are set forward by an hour to make better use of daylight, thereby reducing the consumption of electric lighting.

The United States first implemented DST in 1918 to address World War I but canceled it immediately after the war. During World War II, the US reinstated DST in 1942 and then abolished it again in 1945 after the war ended. In 1966, the US reintroduced DST and established uniform start and end dates, set from the first Sunday in April to the last Sunday in October each year. In 2007, in accordance with the Energy Policy Act, the start date was adjusted to the second Sunday in March, ending on the first Sunday in November.

While most regions in the US observe DST, some areas opt out, including most parts of Arizona (except in the northeast), Hawaii, Puerto Rico, the US Virgin Islands, American Samoa, Guam, and the Northern Mariana Islands.

Trump's Previous Support for DST Cancellation has Warmed

There has been ongoing debate over whether DST should be kept. In March 2022, the US Senate passed a bill proposing to eliminate the twice-yearly time change and instead observe DST year-round starting in 2023. However, the bill was not addressed in the House of Representatives and did not become law.

Last December, former US President Trump publicly expressed support for canceling DST, criticizing it as "troublesome and costly." He stated on social media: "The Republican Party will try their hardest to abolish DST. While it has few supporters, they are very steadfast. DST is inconvenient and costly to the nation."

However, this Thursday, Trump mentioned the time change issue again while signing an executive order, showing a softer stance. He noted, "Some people like DST because they want more light in the evening. But others prefer morning light so children aren't in the dark going to school." He added, "It's a real dilemma. While I can push for a decision, at the moment, support is evenly divided, what can we do?"

The Future of DST Remains Unclear Amid Ongoing Controversy

Although the main goal of DST is to save energy, its effectiveness remains disputed. Numerous studies indicate that time adjustments can harm human health, potentially disrupting circadian rhythms, reducing sleep quality, and increasing the risk of cardiovascular problems. Additionally, there is no academic consensus on the actual energy savings provided by DST.

Discussions about the future of DST continue in American society, with several state governments pushing for legislation to abolish or make DST permanent. Nonetheless, given Congress's slow response to related bills, the future adjustments to DST remain highly uncertain.

For now, the US will continue to follow the current DST plan until new laws are enacted.

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