Changes were originally supposed to go into effect Sunday December 14th, but have been delayed to February 15th 2015. There will be two major changes to the current process:
1. The calculation window is being widened to 5 minutes from one minute currently. The window will start 2.5 minutes before the hour or half hour and end 2.5 minutes after the hour or half hour (depending on the currency).
2. Thomson Reuters Matching trade and order data will be added into the calculation of EUR, JPY, CHF, and RUB.
For more details, please reference these documents: