There shall be no repeat or reopening of panel proceedings. In no case shall a panel retain jurisdiction of any such claim in excess of ninety (90) days from date of commencement of proceedings. If at the end of such ninety (90) day period the panel is unable to decide the issues before it, it shall summarily conclude the proceedings and the members may informally, by written communication, express to the parties their joint and several impressions and conclusions, if any, albeit the same may be tentative or based upon admittedly incomplete consideration; provided, by written agreement of all parties the jurisdiction of the panel, if it concurs therein, may be extended and the proceeding carried on for additional periods of thirty (30) days.