Historically, the changing of clocks was
established by law in 1918 as a fuel
saving measure during World War I.
However, there is a common myth that DST was
established to extend the daylight hours for
farmers. This is not true. Farmers were
extremely opposed to having to turn their
clocks forward and back twice a year.
Changing hours is actually a disruption for
the farmer. Imagine telling a dairy cow
accustomed to being milked at 5:00 a.m. that
their milking time needs to be moved an hour
because the truck is coming to pick up their
milk at a different time! For the farmer,
plants and animals, it is the sun and
seasons which determines their activity.
The 1918 law lasted only seven months. It
proved unpopular with farmers and other
folks. However, after repeal in 1919, some
state and localities continued the
observance.
It took another war, World War II, to
introduce a law by President Franklin D.
Roosevelt, establishing year-round DST. This
“War Time” law lasted from February 9, 1942
to September 30, 1945.
From 1945 to 1966, observance of DST was
quite inconsistent across the states.
There were no uniform rules. This caused
massive confusion in the transportation
and broadcasting industry which pushed for
standardization. Farmers continued to
oppose it.
To address this confusion, permanent DST was
introduced by President Lyndon B. Johnson on
April 12, 1966 and signed into law as the
Uniform Time Act. This established a system
of uniformity within each time zone.
Daylight saving time was the law throughout
the United States and its territories.
However, states were allowed to opt out of
the law, and some did.
From https://www.almanac.com/states-object-changing-clocks-daylig...