Unless otherwise specifically provided by 945 CMR 5.00 or by other applicable law, computation of any time period referred to in 945 CMR 5.00 shall begin with the first day following the act which initiates the running of the time period. When the last day of the period is a Saturday, Sunday, or legal holiday or any other day on which the offices of the Commonwealth are closed, the period shall run until the end of the following business day.