Section 38. District courts and Boston municipal court divisions shall always be open and business may be transacted at any time, except as provided in section six of chapter two hundred and twenty. Sittings of the courts shall be held in the courthouses or other places provided therefor by the judicial branch, at the times and in the towns fixed by law; but if the times are not fixed by law, they shall be prescribed as provided in section fifteen. Sittings may be adjourned from time to time as occasion requires, and cases, civil or criminal, may be continued to any future day fixed for the sitting of the court. Subject to any other provisions of law relative to the filing of complaints for particular crimes, district courts and Boston municipal court divisions may place on file any complaint in a criminal case other than a complaint for the commission of a felony issued against a person who appears previously to have been convicted of a felony or previously to have had a complaint for felony placed on file.