Any advertising device lawfully in existence in an adjacent area on July 1, 1972, which does not conform with the provisions of this subchapter, shall be required to be brought into conformity or removed within six years after July 1, 1972. Any advertising device lawfully erected after said date which subsequently becomes nonconforming, shall be required to be brought into conformity or removed within five years after the date the nonconformity occurs. However, no advertising device shall be acquired or be required to be removed pursuant to this subchapter unless the department has received notification from the federal government that the federal share of just compensation to be paid is immediately available to contribute to the cost of acquisition or removal; this requirement shall not apply to the acquisition or removal of advertising devices for which no federal share is payable.