Standard time refers to sun time, or time one would determine using a sundial. A time zone refers to a region of the Earth that has adopted the same standard time, usually called local time. Time zones were established in the in the U.S. and Canada by the railroads in 1883. But it wasn’t until March 19, 1918 that it was official established as a law, sometimes called the Standard Time Act. This act also established daylight saving time. Daylight saving time was repealed in 1919, but standard time in time zones remained in law. It was re-established during World War II, and after the war some states continued to use it.
The Uniform Time Act of 1966 provided standardization in the dates of beginning and end of daylight time in the U.S. but did not make it mandatory. States or even parts of a state, such as Arizona, have a choice, as they do today.The starting and stopping dates for daylight saving time have changed over the years. In 1974, daylight time began on 6 January and in 1975 it began on 23 February. After those two years the starting date changed back to the last Sunday in April. In 1986, a law was passed that shifted the starting date of daylight time to the first Sunday in April. The Energy Policy Act of 2005 changed the starting date to the second Sunday in March and the ending date on the first Sunday in November. The time on these days officially changes at 2:00 am.
In March, DST starts by setting clocks forward 1 hour. March is the month when spring officially starts, so DST starts by “Springing Forward.” This means you lose an hour. Is this hour actually lost? No. The Earth continues to rotate at the same speed, so there is still basically 24 hours in every day. But those on DST turn their clocks forward one hour. In the fall (autumn) DST ends and the “lost hour” is added. You “Fall Backward,” meaning clocks are set back one hour.