When such collection for a sinking fund is to be applied to the payment of bonds maturing within twelve months from the date of such collection, then such collection to the amount of the bonds so about to mature need not be invested. And such investments need not be made unless the amount on hand for investment shall amount to one thousand dollars, it being the intention of this section and § 11-15-210 that whenever the amount of any sinking fund collected shall be one thousand dollars or more the investment of one thousand dollars or any multiple thereof on hand shall then be made.