Section 15. The chief justice for the district court department, and the chief justice for the Boston municipal court department, shall prescribe the times for holding civil and criminal trials in their respective departments, and the divisions thereof, except where such times are established by law, and the hours when their respective departments, and divisions, shall open for the transaction of business, and shall also prescribe reasonable office hours for the clerks of their respective divisions, during which hours the offices of such clerks shall be open, and may authorize such clerks to operate their offices on Saturdays with reduced personnel. Such hours shall be fixed with reference to the business of said divisions and the convenience of the public and of attorneys, and notice thereof shall be posted in a conspicuous place in the offices of the respective clerks. Clerks shall also keep their offices open whenever the court so orders.