49 CFR § 71.2 - Annual advancement of standard time.
(a) The Uniform Time Act of 1966 (15 U.S.C. 260a(a)), as amended, requires that the standard time of each State observing Daylight Saving Time shall be advanced 1 hour beginning at 2 a.m. on the second Sunday in March of each year and ending at 2 a.m. on the first Sunday in November. This advanced time shall be the standard time of each zone during such period. The Act authorizes any State to exempt itself from this requirement. States in two or more time zones may exempt either the entire State or may exempt the entire area of the State lying within either time zone.
(b) Section 3(b) of the Uniform Time Act of 1966 (15 U.S.C. 260a(b)) provides that “it is the express intent of Congress * * * to supersede any and all laws of the States or political subdivisions thereof insofar as they may now or hereafter provide for advances in time or changeover dates different from those specified in [section 3(a) of that Act]”, which are those specified in paragraph (a) of this section.