Job work transitional relief ensures timely-returned inputs avoid tax, subject to declaration and possible commissioner extension. No tax is payable on inputs or semi-finished goods despatched under prior law to a job worker or other premises and returned after the appointed day if the items are returned within the prescribed period; the Commissioner may extend that period for sufficient cause, but failure to return within the period leads to recovery of input tax credit. The exemption requires the despatcher and job worker to declare details of stock held on the appointed day in the prescribed form, manner and time, and permits transfers to registered persons for supply under existing law within the period.