<P> If they do so, the boundary of that zone is locally shifted to the west; the accumulation of such changes results in the long - term westward trend . The process is not inexorable, however, since the late sunrises experienced by such places during the winter may be regarded as too undesirable . Furthermore, under the law, the principal standard for deciding on a time zone change is the "convenience of commerce". Proposed time zone changes have been both approved and rejected based on this criterion, although most such proposals have been accepted . </P> <P> Daylight saving time was established by the Standard Time Act of 1918 . The Act was intended to save electricity for seven months of the year, during World War I. DST was repealed in 1919 over a Presidential veto, but standard time in time zones remained in law, with the Interstate Commerce Commission (ICC) having the authority over time zone boundaries . Daylight time became a local matter . </P> <P> During World War II, Congress enacted the War Time Act (56 Stat. 9) on January 20, 1942 . Year - round DST was reinstated in the United States on February 9, 1942, again as a wartime measure to conserve energy resources . This remained in effect until after the end of the war . The Amendment to the War Time Act (59 Stat. 537), enacted September 25, 1945, ended DST as of September 30, 1945 . During this period, the official designation War Time was used for year - round DST . For example, Eastern War Time (EWT) would be the equivalent of Eastern Daylight Time during this period . </P> <P> From 1945 to 1966 U.S. federal law did not address DST . States and cities were free to observe DST or not, and most places that did observe DST did so from the last Sunday in April to the last Sunday in September . In the mid-1950s many areas in the northeastern United States began extending DST to the last Sunday in October . The lack of standardization led to a patchwork where some areas observed DST while adjacent areas did not, and it was not unheard of to have to reset a clock several times during a short trip (e.g., bus drivers operating on West Virginia Route 2 between Moundsville, West Virginia, and Steubenville, Ohio had to reset their watches seven times over 35 miles). </P>

When did the usa start using daylight savings time