(b)recovery shall be made of all the duties which have not been paid, but would have been paid had the amendments made by sub-section (1) been in force, within a period of thirty days from the date on which the Finance Bill, 2012 receives the assent of the President and in the event of non-payment of such duties of excise within the said period, interest at the rate of twenty-four per cent, per annum on the amount of such duties in addition to the amount of duties to be recovered, shall be payable from the date immediately after the expiry of the said period of thirty days till the date of its payment;