Mass. Gen. Laws ch. 234A § 41
The length of the term of service for trial jurors shall be one day unless a juror is assigned to or impanelled on an incompleted trial when the term ends or unless the court orders otherwise. Nothing in this section shall prevent a trial juror from serving or participating on more than one trial during his term, except that a trial juror who has participated in the rendering of a verdict shall not be required to participate in a second trial even though the juror may not have completed his first day of juror service at the time of commencement of the second trial. Jurors in the juror pool awaiting assignment to a trial shall be discharged as early in the afternoon as possible after it has been determined that their services as jurors will not be needed. The length of the term of service for grand jurors shall be three months unless the court enlarges such term. The court shall have authority to enlarge grand jurors' terms of service upon a finding that the efficient administration of justice requires such enlargement.
Mass. Gen. Laws ch. 234A, § 41