Provisional assessment finalisation sets document submission deadlines, extension hierarchy, finalisation procedures and penalty for non-compliance. Regulations create a procedural framework for finalising provisional assessments under the Customs Act: required documents or information must be produced within prescribed periods with written requisitions; a tiered extension regime allows the proper officer, Additional/Joint Commissioner, and Commissioner to extend time for reasons recorded; the proper officer must finalise assessments within a set period from receipt of required material or intimation, subject to Commissioner-authorised extension; finalisation follows section 18, permits adjustment from security, requires speaking orders if final assessment differs, and mandates cancellation of bonds and return of security if no dues remain.