Earliest is second week of august. Latest is 3rd week of august.
"Around the second or third week of August (no later than August 17 globally), after you’ve had time to play around with the patch and get a feel for the changes, some angry invaders are going to start dropping out of the skies over Azeroth."
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?? Blizzard already said invasions wont happen before the 2nd week of august.