So Wano is predicted/expected to begin in October. We still need to get to the Reverie, assuming we're still following that schedule. That means we have all of August, September, and I guess at most 3 weeks in October to finish up WCI and touch on the Reverie. Since there's no chapter this week or two weeks from now (right?), that means we'll get like 4 chapters in August and 4 in September. That's at most a total of 11 chapters to wrap up WCI and go into the Reverie. And that's not to mention any more breaks we might have.
I imagine Oda's planning the Reverie to all be contained in it's own volume for the most part. Volume 86 will likely have Chapters 859 through 868/869 with the cliffhanger of either Big Father or Big Mom attacking Big Father over his betrayal. Then we have 5 or 6 chapters that will head into Volume 87. If Volume 87 is the final volume of WCI, then it'll probably have Chapters 869/870 through 878/879. That leaves about 5 or 6 chapters for Luffy and co. to finish things up in Totland, which means about 5 or 6 chapters for the Reverie, which I imagine is gonna be what we see while Luffy head towards Zou and/or Wano to regroup.
All of this was some handwavy math, probably shouldn't have tried to figure all this out, especially since I'm being super optimistic with no other breaks and stuff.