Ready or not, we transition to daylight saving time at 2:00 AM on Sunday, March 13. Check to see which clocks you need to set ahead one hour before retiring on Saturday night; some devices will update on their own, but not all. Properly speaking, local civil time will advance from 1:59:59 AM EST (Eastern Standard Time) to 3:00:00 AM EDT (Eastern Daylight Time). This shift in our timekeeping practice will cost us an hour on Sunday and give us an excuse for being late to almost anything for the next few days. Cosmic time, itself, will be completely unaffected by how we choose to count its inexorable progression.

The American Academy of Sleep Medicine suggests preparing for the change a few days in advance. Moving your bedtime and other daily routines forward a few minutes at a time to avoid a sudden, disconcerting shift over a single night. They also suggest going outside early on Sunday morning so that the sunlight can help reset your internal body clock.

After an abortive experiment in 1918, Congress re-established national daylight saving time during World War II. The nation observed permanent daylight saving time from February 9, 1942 through September 30, 1945. After the War, daylight saving time was a local option. The Uniform Time Act of 1966 set national start and end times for daylight saving time although individual states and territories can decide whether to participate. We currently follow the dates enacted by The Energy Policy Act of 2005: start on the second Sunday in March and end on the first Sunday in November.

Hawaii, American Samoa, Guam, Puerto Rico, and the U.S. Virgin Islands abstain from daylight saving time. The situation in Arizona is complicated. Although Arizona and the Hopi Nation do not change their clocks, the Navajo Nation does. On the opposite extreme, 18 states have expressed interest in year-round daylight saving time. So far, Virginia legislators have expressed little interest in such proposals.

Daylight saving time is occasionally promoted as an energy saving measure. In 2008, the Energy Department found a 0.5% reduction in total consumption of electricity during the four extra weeks of daylight saving time. However, such savings may not be as significant during the height of summer when the demands for air conditioning and other cooling measures are higher. A study of residential electricity in Indiana over the entire daylight saving period found a 1% increase in energy use.