Blizzard have clarified the exact release time for the Naxxramas raid and Scourge Invasion event in Season of mastery.
SoM (Source)
We’ve seen some questions on this. Please know that in Season of Mastery, the Naxxramas raid and the Scourge Invasion will begin:
23:00 BST on Thursday, July 28 / 00:00 CEST on Friday, July 29