(2)At the close of each quarter, or as soon thereafter as may be convenient, the duty collected under sub-section (1) shall, after deducting the expenses of collection (if any), be paid by the Customs Collector to the Board.[(3) After the commencement] of [the Constitution] a duty shall only be leviable under this section if it [was lawfully levied] immediately before that date, and shall only be leviable until provision to the contrary is made by [Parliament].
