There is a 9-time zone in the Time Zone Map of the USA and its dependencies. All-time zone boundaries and DST observance are looking after by the Department of Transportation. Daylight Saving Time (DST) begins at 2:00 a.m. local time on the second Sunday in March. It moves the clocks forward one hour for making better use of daylight. On the first Sunday in November areas on Daylight Saving Time return to Standard Time at 2:00 a.m. All-time zones in the United States and its regions are defined at the federal level by law 15 USC §260.
Full-Time Zone Table of USA