The total length of a detail or several details combined must not exceed 5 consecutive years, except that when the Secretary of State, on the recommendation of the head of the agency, determines it to be in the national interest, the 5 years allowed for details may be extended for up to an additional 3 years. A detail or combination of details and transfers must not exceed 8 years in the aggregate throughout an employee's Federal career.
5 C.F.R. §352.306