Provides that the director shall determine when interest, if provided by a plan, shall be credited to accounts in the public employees' retirement system, the teachers' retirement system, the school employees' retirement system, the public safety employees' retirement system, the law enforcement officers' and firefighters' retirement system, or the Washington state patrol retirement system. The amounts to be credited and the methods of doing so shall be at the director's discretion, except that if interest is credited, it shall be done at least quarterly.