I'm not a lawyer. Under the Fair Labor Standards Act, comp time should begin to accrue after 40 hours worked in a week. However, because you work for a government agency, the rules may be different as they apply to your work week.
This is a link to a .PDF file with answers to frequently asked questions about overtime and comp time under the FLSA.
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This may be an issue you wan to contact an Overtime/ Wage and Hour lawyer about near you immediately. They would best know the law.