310 CMR, § 5.07
Unless otherwise specifically provided by statute, 310 CMR 5.00, or any determination issued pursuant to 310 CMR 5.00, any time period prescribed or referred to in 310 CMR 5.00 or in any determination issued pursuant to 310 CMR 5.00 shall begin with the first day following the act which initiates the running of the time period, and shall include every calendar day, including the last day of the time period so computed. If the last day is a Saturday, Sunday, legal holiday, or any other day in which the Department's offices are closed, the deadline shall run until the end of the next business day. If the time period prescribed or referred to is six days or less, only days when the offices of the Department are open shall be included in the computation.
310 CMR, § 5.07