For each employee subject to the partial overtime exemption in
section 7(k) of the Act, a public agency which is a State, a political
subdivision of a State, or an interstate governmental agency shall
maintain and preserve records containing the information and data
required by Sec. 553.50 and, in addition, make some notation on the
payroll records which shows the work period for each employee and which
indicates the length of that period and its starting time. If all the
workers (or groups of workers) have a work period of the same length
beginning at the same time on the same day, a single
notation of the time of day and beginning day of the work period will
suffice for these workers.