(a) For the purpose of this part the word night shall mean the time between 5 p.m. of any day and 8 a.m. of the following day.

(b) The term holiday shall mean only national legal public holidays, viz., January 1, February 22, May 30, July 4, the 1st Monday in September, November 11, the 4th Thursday in November, December 25, and such other days as may be declared legal public holidays by an act of Congress or by an Executive order of the President of the United States.

(c) The term Sunday shall include the first day of each calendar week.