Rest periods of short duration, running from 5 minutes to about 20
minutes, are common in industry. They promote the efficiency of the
employee and are customarily paid for as working time. They must be
counted as hours worked. Compensable time of rest periods may not be
offset against other working time such as compensable waiting time or
on-call time. (Mitchell v. Greinetz, 235 F. 2d 621, 13 W.H. Cases 3
(C.A. 10, 1956); Ballard v. Consolidated Steel Corp., Ltd., 61 F. Supp.
996 (S.D. Cal. 1945))