Most of the US state of Arizona does not use Daylight Saving Time (DST). The exception is the Navajo Nation.
With the exception of the Navajo Nation, Arizona does not set the clocks forward 1 hour in spring for DST with the rest of the United States.
Mountain Standard Time
Almost all of Arizona is on the same time zone, Mountain Standard Time (MST), all year. The time zone has a UTC offset of minus 7 hours (UTC-7).
It is also known as Mountain Time, but that term refers both to standard time and the time zone which is elsewhere used during DST: Mountain Daylight Time (MDT).
Navajo Nation Uses DST
The Navajo Nation, a semi-autonomous Native American territory, follows the United States DST schedule. It lies in northeastern Arizona, northwestern New Mexico, and southeastern Utah.
During DST the Navajo Nation, which includes the towns of Tuba City, Chinle, and Window Rock, sets the clocks forward 1 hour to Mountain Daylight Time (MDT), which is 6 hours behind UTC (UTC-6).
No DST in Hopi Nation
A part of the Hopi Nation, which lies within the Navajo Nation, follows Arizona’s no-DST rule. To confuse matters more, there is also an even smaller Navajo Nation territory within the Hopi Nation within the Navajo Nation. In addition to this, there is another Hopi area adjacent to the main Hopi Nation territory.
As a result, if driving the correct route from the Arizona state border through both Navajo and Hopi areas to the other side one can end up changing one’s clock 7 times! For example: Tuba City (Navajo) and Moenkopi (Hopi) are only a couple of miles apart, but they have a 1-hour time difference during the summer. Jeddito (Navajo), in the middle of Hopi Nation territory, is 1 hour ahead of the surrounding areas during summer.
Opted out of DST
Arizona is exempt from DST according to the US Energy Policy Act of 2005. The Act gives every state or territory the right to decide if it wants to use DST. If DST is observed, the state has to schedule DST in sync with the rest of the US: From the second Sunday in March until the first Sunday in November.
Because of Arizona’s hot climate, DST is largely considered unnecessary. The argument against extending the daylight hours into the evening is that people prefer to do their activities in the cooler evening temperatures.
Note qu’avant la standardisation de 1977, c’était la même chose à l’échelle du pays tout entier, chaque état voire chaque comté se déterminait indépendamment des autres…
(histoire compliquée, détaillée dans l’article WP ci-dessous.