310 CMR, § 80.06
Unless otherwise specifically provided by law, 310 CMR 80.00, or any determination issued pursuant to 310 CMR 80.00, any time period prescribed or referred to in 310 CMR 80.00, or in any determination issued pursuant to 310 CMR 80.00, 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 offices of the Department are closed, the deadline shall run until the end of the next business day. If the time period prescribed or referred to is less than seven days, only days when the offices of the Department are open shall be included in the computation. If the time period is prescribed in hours, the computation is the exact number of hours from the start of the deadline without regard to whether the Department is open, unless the deadline requires delivery of information or documentation to the Department, in which case it is on the next business day after the running of the deadline if that deadline runs on a day when the Department is closed.
310 CMR, § 80.06