There are totally 9 time zones in United States, four in the mainland, one in Alaska, one in Howaii, and the other three in oversea territories.

Four time zones in the mainland are: Eastern Standard Time、Central Standard Time、Mountain Standard Time、Pacific Standard Time

Daylight Saving Time in United States begins on the second Sunday in March, and ends on the first Sunday of November. Take 2017 as an example, United States observes DST on March 12th, and ends on November 5th.

It is worth nothing that, some parts of United States don't observe Daylight Saving Time, including most of Arizona except the Navajo Nation Community, Howaii, American Samoa, Guam, Puerto Rico and the U.S. Virgin Islands.