Use of standard time gradually increased because of its obvious practical advantages for communication and travel. Standard time in time zones was not established in U.S. law until the Standard Time Act of 1918 of March 19, 1918, also known as the Calder Act (15 USC 260). The act also established daylight saving time, itself a contentious idea.
when did daylight saving time start in the usa
March 19, 1918