And whereas inconveniences and confusion might arise from the executor, assignee, or other person or persons having right to the claim arising from money expended by the proprietor of an entailed estate in the improvement thereof, their not timeously requiring the heir next succeeding in the estate to pay what they are entitled to receive by authority of this Act, and suing such heir to compel him to pay, if payment is not made: For remedy whereof, the executor, assignee, or other person or persons having right to the claim arising from money expended by the proprietor of an entailed estate in the improvement thereof, shall be obliged, within the space of two years after the death of the proprietor who expended the money, to require payment from the succeeding heir; and within the space of six months after the lapse of the said two years to institute an action if the money is not paid, in the Court of Session; and to proceed without delay in recovering a decree for the sum due, and doing exact diligence for recovering payment thereof, or at least to the amount of one third part of the free rents of the estate which shall have become due to such succeeding heir.