Provisional customs assessment: two year limit with possible one year extension; timelines for document submission, finalisation, and penalties. The guidelines impose staged timelines for finalising provisional assessments: requisition missing documents within 15 days; importer/exporter to furnish within two months with possible two month extension by the proper officer and further extension by a superior officer up to a 14 month cap for submission. Finalisation should occur within three months after receipt or expiry of time or enquiry conclusion, with serial two month extensions permitted but not beyond an absolute two year limit from provisional assessment, extendable by one year by the Principal Commissioner for sufficient cause.