When the commissioner desires to take property for highway purposes and has entered into an agreement to purchase at a stipulated amount any real estate or any interest therein which appears of record with the owner or owners thereof and the amount agreed to be paid for such property or interest is not paid within ninety days from the date when the owner or owners of such property file with the commissioner a notice in writing of acceptance of such agreement, interest at eight per cent per annum shall be paid on such amount by the state unless the property owner fails to furnish clear title within such ninety days. Such interest shall commence to accrue at the end of such ninety-day period, whether or not an assessment has been filed as provided in subsection (b) of section 13a-73. Whenever the state enters into possession of property being condemned prior to the date of execution of such an agreement, such interest shall commence to accrue from the date of actual taking of possession by the state.