It's that time of year again: Many Americans will have to reset their clocks and circadian rhythms when daylight saving time ends on Sunday.

That means, in most states, lighter mornings and darker evenings.

At 2:00 a.m. on Sunday, the time for millions across the country will jump back one hour – an adjustment that has been both welcomed by those seeking extra sleep time or criticized by those who see it as an inconvenience.

Here is what you should know.

How many states observe daylight saving time?

Every U.S. state observes daylight saving time except for Hawaii and Arizona, according to the National Conference of State Legislatures (NCSL). The portion of the Navajo Nation that's in Arizona, however, does observe daylight saving. U.S. territories Guam, Puerto Rico, American Samoa

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