Congress passed The 1918 Standard Time Act which imposed a single time zone nation-wide during World War I.  After the war, the nation abandoned the single time zone effort.  During World War II, "war time" legislation required that standard time be pushed ahead one hour in each time zone in an effort to conserve fuel. While the legislation was repealed in September, 1945, multiple states continued the practice of moving their clocks one hour forward in the Spring and one hour back in the Fall.  Between 1966, when Congress passed standard time legislation, and 2006, Daylight Saving Time was observed from the first Sunday in April to the last Sunday in October.

The Energy Policy Act of 2005 changed that schedule, with the change to be implemented in 2007.  Effective March 11, 2007, Daylight Saving Time will begin three weeks earlier, on the second Sunday in March, and end a week later, on the first Sunday in November.