Based on that fact, it looks like it may be the last Friday of the month - 5/27 because if it was a different Friday of the month why have the "drop-dead" date be 5/31.
laranger In regard to when the ICC Court meets, from the Foreword to the ICC Rules of Arbitration
"Every ICC arbitration is conducted by an arbitral tribunal with responsibility for examining the merits of the case and rendering a final award. Each year, ICC arbitrations are held in numerous countries, in most major languages and with arbitrators from all over the world. The work of those arbitral tribunals is monitored by the ICC Court, which meets weekly all year round. Composed of members from over 80 countries, the Court organizes and supervises arbitrations held under the ICC Rules of Arbitration. The Court must remain constantly alert to changes in the law and the practice of arbitration in all parts of the world and must adapt its working methods to the evolving needs of parties and arbitrators. For the day-to-day management of cases in many languages, the ICC Court is supported by a Secretariat based at the headquarters of the International Chamber of Commerce, in Paris."
I just talked to NY, who said the following: Once a decision is in final form (all the T's crossed), the Paris office meets in plenary session to give its final blessing to panel decisions. These meetings are held on Friday. However, the party did not know whether it was the lst, 2nd Friday, etc., and said we should call Paris to get the exact information. Bottom line: Friday appears to be the day, but only once a month, rather than 4 times.