Posted on MMO Champion:
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To access the new Raid Finder wings, you’ll need a minimum average Item Level (ilvl) of 496 or higher.

This is the current schedule based on the planned patch release date of September 10. If we determine any changes are needed, we’ll update this article.

September 10 – Patch 5.4 Release
Normal
Flex Wing 1 “Vale of Eternal Sorrows”

September 17
Heroic (Normal Garrosh kill required)
Flex Wing 2 “Gates of Retribution”
Raid Finder Wing 1 “Vale of Eternal Sorrows”

September 24
Raid Finder Wing 2 “Gates of Retribution”

October 1
Flex Wing 3 “The Underhold”

October 8
Raid Finder Wing 3 “The Underhold”

October 15
Flex Wing 4 “Downfall”

October 22
Raid Finder Wing 4 “Downfall”