It takes a little work, but based on Raphus' post you can determine an ETA.
He said that they will be holding off on an update because of the hotfix. They are waiting until the EU servers come back up from maintenance. It also says that it will be a few hours after EU servers come up. Based on that information I checked the EU maintenance schedule on their forum:
May 21st from 5am-11am CEST. CEST is 6 hours ahead of EDT, so EU maintenance is scheduled to end at 5am Eastern Daylight Savings Time. Add a couple of hours to that for testing and the ETA I have come up with is 7am EDT.
7 a.m. EDT, and possibly longer if there are any issues.