29 C.F.R. § 553.50

For each employee subject to the compensatory time and compensatory time off provisions of section 7(o) 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 basic information and data required by § 516.2 of this title and, in addition:

(a) The number of hours of compensatory time earned pursuant to section 7(o) each workweek, or other applicable work period, by each employee at the rate of one and one-half hour for each overtime hour worked;

(b) The number of hours of such compensatory time used each workweek, or other applicable work period, by each employee;

(c) The number of hours of compensatory time compensated in cash, the total amount paid and the date of such payment; and

(d) Any collective bargaining agreement or written understanding or agreement with respect to earning and using compensatory time off. If such agreement or understanding is not in writing, a record of its existence must be kept.