Section 6. The divisions of the departments of the trial court shall always be open and the business thereof, or of a justice thereof, may be transacted at any time, except that such business shall not be transacted on a Saturday or Sunday or on a legal holiday unless it relates to an application which, in the opinion of the justice to whom it is made, is of pressing necessity or for the purpose of instructing or discharging a jury, receiving a verdict or adjourning; provided that, if the convenience of the public so requires, the divisions shall be open for the transaction of business on such Saturdays, not legal holidays and during such hours thereof as the administrative justice of the department may determine. This section shall not prevent the exercise of the jurisdiction of any magistrate in criminal cases to preserve the peace or arrest offenders. The provisions of section nine of chapter four shall apply in the case of the closing of a court on any Saturday to the same extent as if such Saturday were a legal holiday.