Most of the nation falls back at 2 a.m. Sunday, Nov. 6, when daylight saving time ends.
Time-keepers in all but two states — Arizona and Hawaii — will set clocks back an hour.
DST is a concept that has been around since at least Colonial days, and, as a tool to conserve energy, became part of the U.S. way of life during WWI and WWII.
DST was observed from April through mid-October until 2007, when Congress adjusted the period to begin three weeks earlier and end a week later to increase energy conservation. The U.S. Energy Department estimates that electricity use decreases by 0.5 percent per day during DST, which adds up to 1.3 billion kilowatt hours, enough to power about 122,000 average homes for a year.
But some science suggests that the time changes negatively impact the duration and quality of sleep — for days for most people, but for longer periods for those vulnerable to sleep deprivation.
For planners, daylight saving time resumes at 2 a.m. Sunday, March 11, 2012.