When can county employees use their comp time?

Q. I am a county clerk and we have some exempt employees who are counting the number of hours they work over 40 hours per week and then add them together, weeks later, and try to take the time off at that time. Doesn’t the Fair Labor Standards say you have to take the time off in the same week or an adjoining week? I can't find the information on this. --  Cynthia, Maine