The "de minimis" worktime concept is a common-sense, court-recognized notion dating from the federal Fair Labor Standards Act's earliest days. It has been articulated by the U.S. Labor Department this way:
In recording working time...,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. * * * 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.
https://www.fisherphillips.com/Wage-and-Hour-Laws/The-Death-of-De-Minimis-Is-Greatly-Exaggerated
In recording working time...,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. * * * 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.
https://www.fisherphillips.com/Wage-and-Hour-Laws/The-Death-of-De-Minimis-Is-Greatly-Exaggerated