Limitation for recovery of excise duty tightened; officers must determine duty within prescribed periods and voluntary payments regulated. Amendment requires the Central Excise Officer, after a notice under section 11A, to determine duties arising from fraud, collusion, willful mis-statement, suppression of facts or contravention intended to evade duty within one year and other duties within six months. A person may voluntarily pay duty before notice and inform the officer, who then will not serve a notice for that duty except to determine any remaining short payment; voluntary payment is excluded where the non-payment arose from fraud or similar misconduct. Interest is payable on amounts paid and any later determined short payment.