Trial juror service shall be for a one-day term unless a juror is assigned to or impaneled on an incompleted trial when the one-day term ends, or unless the court orders otherwise. Nothing shall prevent a trial juror from serving on more than one jury or participating in more than one trial during the term; except that a trial juror whose deliberation ended with a verdict shall not be required to participate in a second trial even though the juror may not have completed the first day of juror service at the time of the commencement of the second trial. Jurors awaiting assignment to a trial shall be discharged as early as possible after it has been determined that their services will not be needed. Grand juror service shall be for a term of twelve months unless the court discharges the jurors earlier or enlarges such term upon a finding that the efficient administration of justice so requires; except that in no event shall a grand jury serve for longer than eighteen months.