Drawback claim time limits: extensions by Assistant Commissioner possible; further relief only via rule 17 relaxation application. Drawback claims must be filed within three months from the Shipping Bill let-export order; the Assistant Commissioner may allow a further three-month extension on sufficient cause, and claims in respect of pre-commencement exports were subject to a three-month window from rules' commencement. Claims filed after the applicable cut-off are time-barred and cannot be accepted by Customs. Relief beyond these limits may be sought under rule 17 by applying to the Commissioner of Drawback with reasons showing failure was beyond the exporter's control.