Daylight Saving Time begins in the U.S. early Sunday morning as the nation switches its clocks forward an hour, according to the National Institute of Standards and Practices.

DST starts on the second Sunday of March and ends the first Sunday in November. The first time switch was officially observed in 1918.

However, DST isn't mandatory since states like Arizona and Hawaii, along with territories like Puerto Rico and Guam, don't change their clocks.

Most phones, computers and radio-controlled clocks typically switch times automatically.