Computation of any period of time referred to in950 CMR 103.00 et. seq. shall begin with the first day following that on which the act which initiates such period of time occurs. When the last day of the period so computed is a day on which the offices of the Division are closed, the period shall run untilthe end of the following business day. When such period of time, with the intervening Saturdays, Sundays, and legal holidays counted, is five days or less, then said Saturdays, Sundays, and legal holidays shall be excluded from the computation; otherwise such days shall be included in the computation.