Daylight saving time (DST) begins on the second Sunday in March and ends on the first Sunday in November. During this period, clocks in most parts of the United States are set 1 hour ahead of standard time. First introduced in the United States in 1918 to mimic policies already being used in several European countries during World War I, DST was unpopular and abolished as a federal policy shortly after World War I ended.1 It was reinstated in 1942 during World War II but covered the entire year and was called “war time.” After World War II ended, it became a local policy. Varying DST policies across cities and states led to the Uniform Time Act of 1966, which mandated DST starting on the last Sunday in April until the last Sunday in October. States were allowed to exempt themselves from observing DST (including parts of the state that were within a different time zone [eg, Michigan and Indiana]).
Malow BA, Veatch OJ, Bagai K. Are Daylight Saving Time Changes Bad for the Brain? JAMA Neurol. 2020;77(1):9–10. doi:10.1001/jamaneurol.2019.3780
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