Blizzard have said that it may start one month either side of one year after the opening of the SoM realms.
That’s all the information we have. Which means it could be in the next week, but don’t expect that, it’s a hope really.
Personally I’m expecting it in the first week of November and posting here will just get you a generic reply saying something like “We have nothing to announce about this, we will let you know when we do.”