This is what Blizzard had to say about the when Patch 7.2 content will be released.

We’ve seen some confusion around the availability and timing of various aspects of the 7.2 patch, and we’d like to clarify our plans for releasing the remaining pieces of Patch 7.2’s content:

  • Week 2 (next week): Legion Assaults begin, first PvP Brawl becomes available

  • Week 3: Chapter 5 of the Class Order Hall campaign unlocks, which activates new followers, new Order Hall upgrades, and class-specific World Quests

  • Week 4-11: Ongoing story pieces unlock, leading up to the eventual opening of the Tomb of Sargeras raid, and the ability to earn Class Mounts

That would appear to indicate that The Tomb of Sargeras raid looks set to open around mid June.