Notice for payment of duties: limitation periods defined, fraud extends recovery window and stays excluded from time. Substitution prescribes that a proper officer may serve notice to recover unpaid, short-levied or erroneously refunded customs duties and interest, require show-cause responses, consider representations, determine amounts due (not exceeding the notice) and require payment; it prescribes distinct limitation periods with an extended period where collusion or willful misstatement or suppression occurred and excludes court-ordered stay periods from limitation, and it defines the relevant date for computation including clearance order, adjustment after provisional assessment, refund date, and payment date.