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]).

夏令时（DST）从3月的第二个星期日开始，到11月的第一个星期日结束。在此期间，美国大部分地区的时钟都比标准时间提前1小时。DST最早于1918年在美国推出，以模仿第一次世界大战期间已在多个欧洲国家使用的政策，但DST在第一次世界大战结束后不久就不受欢迎，并作为联邦政策被废除了。^1个它于1942年在第二次世界大战期间恢复使用，但涵盖了整整一年，被称为“战争时期”。第二次世界大战结束后，这成为地方政策。各个城市和州不同的DST政策导致了1966年的《统一时间法》，该法规定DST从4月的最后一个星期日开始，直到10月的最后一个星期日。允许各州免于遵守DST（包括在不同时区的部分州（例如，密歇根州和印第安纳州））。