244.61. The by-law may(1) prescribe that a unit of assessment or non-residential premises be taken into consideration for the purposes of abatement only if they are vacant for the number of days it fixes, specify whether the days taken into account in computing the number must occur consecutively and, in such a case, whether the days must be included in a single fiscal year or whether they may be included in two fiscal years and specify whether the unit or premises, once a number has been reached, are to be taken into consideration for the purposes of abatement from the day the number is reached or from the first of the days, consecutive or not, as the case may be, included in the fiscal year for which abatement is granted;
(2) prescribe the rules, including verification measures, to be used to establish whether or not the vacancy exists and whether or not the average percentage of unoccupancy is attained;
(3) provide for interest to be added to the amount of a tax supplement or overpayment which must, in the circumstances described in subparagraph 3 of the first paragraph of section 244.60, be paid or refunded.