It's time! This Sunday morning, most of the United States begins Daylight Saving Time at 2 a.m. In the U.S., each time zone switches at a different time.
Daylight Saving Time commences at 2 a.m. to minimize disruption. According to webexhibits.org, the time was originally chosen as the changeover time because it was practical and minimized disruption. Most people were at home and this was the time when the fewest trains were running. It is late enough to minimally affect bars and restaurants, and it prevents the day from switching to yesterday, which would be confusing. It is early enough that the entire continental U.S. switches by daybreak, and the changeover occurs before most early shift workers and early churchgoers are affected.
Many fire departments encourage people to change the batteries in their smoke detectors when they change their clocks because Daylight Saving Time provides a convenient reminder.