Permanent time observation in the United States

Establishing either permanent standard or daylight saving time (DST) eliminates the practice of semi-annual clock changes, specifically the advancement of clocks by one hour from standard time to DST on the second Sunday in March (commonly called "spring forward") and the retardation of clocks by one hour from DST to standard time on the first Sunday in November ("fall back"). The existing practice of switching the clocks twice a year is unpopular, with only about 20% of Americans preferring it. The Uniform Time Act of 1966 formalized the specification of time zones and the dates of DST observation in the United States. Prior to this law, time zones and DST observation in America were independent and erratic across states and cities. The law requires states to change clocks semiannually between standard time and DST on federally mandated dates, and it permits states to opt out of DST observation altogether and remain on permanent standard time, but does not permit observation of permanent DST. Arizona (with the exception of the Navajo Nation), Hawaii, and all permanently inhabited territories observe permanent standard time. Studies have shown the semi-annual clock changes result in sleep disturbances, ultimately resulting in more health problems and traffic accidents. Legislators in 25 states have attempted to switch to either permanent standard time or permanent DST. As of 2023 more states are pursuing permanent DST.