For most of the U.S., daylight-saving time clocks move back one hour to standard time at 2 a.m. Sunday, Nov. 1, 2009, local time. It goes back to daylight savings time the first Sunday of March at 2 a.m.
Congress passed a law, which takes effect in 2007, changing the dates of daylight-saving time so it starts three weeks earlier and will end one week later.
Previously, the start and end dates were the first Sunday in April and the last Sunday in October.
In the U.S., the changeover time was chosen to be 2 a.m., when most people are at home and, originally, the time when the fewest trains were running. This is practical and minimizes disruption. It is late enough to minimally affect bars and restaurants, and prevent the day from switching to yesterday (which would be confusing). It is early enough that the entire continental U.S. has switched by daybreak, and the changeover occurs before most early shift workers and early churchgoers (particularly on Easter) are up and out.
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