Mass. Gen. Laws ch. 279 § 6A
When a person is sentenced on a first offense to imprisonment in a jail or house of correction for a term which does not exceed one year, the court may order the sentence to be served in whole or in part on weekends and legal holidays or such other periodic interval as the court may determine. Such a sentence shall be known as a special sentence of imprisonment. If an offender receives a special sentence of imprisonment under this section, he shall, unless otherwise provided by the sentence of the court, report to the institution to which he has been sentenced no later than 6:00 p.m. on Friday and shall be released at 7:00 a.m. on the succeeding Monday; provided, however, that if the succeeding Monday is a holiday, the offender shall not be released until 7:00 a.m. on Tuesday; and provided further, that the total time served shall be equal to the sentence imposed.
On application of the offender, of the department of correction or the director of the institution to which the offender is committed, or on its own motion, the court may after a hearing rescind or modify an order under the first paragraph, and may direct that the balance of the sentence of imprisonment shall be served consecutively. Before a special sentence is rescinded or modified, the court shall cause the notification thereof to be given to the district attorney and to the offender.
If while serving such a special sentence, such person is convicted of a subsequent crime other than a nonmoving motor vehicle violation, the terms of said special sentence shall be rescinded and said person shall complete the balance of his original sentence consecutively in the jail or house of correction in which he has been serving said special sentence.
Mass. Gen. Laws ch. 279, § 6A