So Blizzard released patch 7.2 well before the tomb of Sargeras opened, which leads one to believe that they might do the same with patch 7.3.
Do you think that Patch 7.3 could be released in September? That would give the Tomb of Sargeras raid 3-4 months of being current tier before the 7.3 patch is released, and if they do a similar time release of the 7.3 raid, it would mean that Tomb would have been out for 5-7 months before the next raid is released depending on how long the lead up to the 7.3 raid is.
So:
7.2.5 - Early June (Tomb of Sargeras Opens)
7.3.0 - Late September
7.3.5 - Late December (Argus Raid Opens)
What do you think?