If the obstruction or excavation of the right-of-way begins later or ends sooner than the date given on the permit, the permittee shall notify the Building Inspector of the accurate information as soon as this information is known. If the obstruction of a right-of-way is of a shorter duration than that estimated on the permit application, the Building Inspector will, upon request, refund or credit to the permittee a proportionate amount from that part of the permit fee which was based on the duration of the obstruction.