5 CFR §301.203

1. (a)An appointment under this subpart is of indefinite duration unless otherwise limited.
2. (b)An agency may make an overseas limited term appointment for a period not in excess of 5 years when a time limitation is imposed as a part of a general program for rotating career and career-conditional employees between overseas areas and the United States after specified periods of overseas service.
3. (c)An agency may make an overseas limited appointment for 1 year or less to meet administrative needs for temporary employment. An agency may extend such an appointment for up to a maximum of 1 additional year.
4. (d)Upon request from the headquarters level of a Department or agency, OPM may approve, or delegate to agencies the authority to approve, exceptions to the time limits set out in paragraph (c) of this section.