Its intended effect was to simplify the official pattern of where and when daylight saving time (DST) is applied within the U.S.

[2] The law was later amended again in 1986 to move the uniform start date for DST to the first Sunday in April (effective 1987).

The latest amendment, part of the Energy Policy Act of 2005, extends DST by four or five weeks by moving the uniform start date for DST to the second Sunday in March and the end date to the first Sunday in November (effective 2007).

The Department of Energy was required to report to Congress the impact of the DST extension by December 1, 2007 (nine months after the statute took effect).

[5] Arizona has not observed daylight saving since the year following the enactment of the Uniform Time Act of 1966.