The National Park Service relies on seasonal employees to make our parks better places for visitors. NPS/Connar L'Ecuyer. Starting May 26, 2018, to be able to be rehired the following service year without having to compete again for a similar temporary seasonal position, seasonal employees must work no more than a combined total of 1,039 hours anywhere in the National Park Service (NPS) within their service year. This change follows an audit of the NPS hiring and human resource practices by the U.S. Office of Personnel Management (OPM).