29 C.F.R. § 785.47

In recording working time under the Act, insubstantial or insignificant periods of time beyond the scheduled working hours, which cannot as a practical administrative matter be precisely recorded for payroll purposes, may be disregarded. The courts have held that such trifles are de minimis. (Anderson v. Mt. Clemens Pottery Co., 328 U.S. 680 (1946)) This rule applies only where there are uncertain and indefinite periods of time involved of a few seconds or minutes duration, and where the failure to count such time is due to considerations justified by industrial realities. An employer may not arbitrarily fail to count as hours worked any part, however small, of the employee's fixed or regular working time or practically ascertainable period of time he is regularly required to spend on duties assigned to him. See Glenn L. Martin Nebraska Co. v. Culkin, 197 F. 2d 981, 987 (C.A. 8, 1952), cert. denied, 344 U.S. 866 (1952), rehearing denied, 344 U.S. 888 (1952), holding that working time amounting to $1 of additional compensation a week is “not a trivial matter to a workingman,” and was not de minimis; Addison v. Huron Stevedoring Corp., 204 F. 2d 88, 95 (C.A. 2, 1953), cert. denied 346 U.S. 877, holding that “To disregard workweeks for which less than a dollar is due will produce capricious and unfair results.” Hawkins v. E. I. du Pont de Nemours & Co., 12 W.H. Cases 448, 27 Labor Cases, para. 69,094 (E.D. Va., 1955), holding that 10 minutes a day is not de minimis.