When do the clocks change?

US daylight saving runs from the second Sunday in March to the first Sunday in November, fixed by the Energy Policy Act of 2005. Clocks move at 2am local time in each zone, not simultaneously across the country — so the change sweeps west, reaching Hawaii three hours after New York, except that Hawaii does not take part.

In March 2am becomes 3am and the hour between never exists; a timer set for 2:30am that morning has no moment to fire. In November 1:59am is followed by 1:00am and the hour happens twice, which is why timestamps that day need an offset and not just a clock reading.

Arizona and Hawaii do not observe daylight saving, which is why “what time is it in Arizona” is the most-searched question in this whole cluster — Arizona matches Pacific Time in summer and Mountain Time in winter, so the answer depends on the month in a way it does not anywhere else.

Current time in Arizona. Current time in Hawaii. The Navajo Nation, inside Arizona, does observe it — and the Hopi Reservation, inside the Navajo Nation, does not.

Of the 246 countries with a time zone of their own, 179 never change their clocks — 73% of them. Daylight saving is largely a European and North American habit, and the countries that keep it do not all change on the same day.

60 change everywhere, and 7 change in part of the country only — Antarctica, Australia, Canada, Chile, Greenland, Mexico, Ukraine. Mexico is the clearest case: it stopped changing its clocks in 2022 apart from the municipalities on the US border, which kept the change so that the two sides of the line stay on the same clock.