Well it took them something like a year of sailing before they reached Shabondy... It would be hard to make a plausible plot that got them together a lot sooner than that.

I guess they could meet at Reverse Mountain, since it's between the Four Seas. That would cut some time down. But Luffy has to sail from Marinford. Kuma doesn't seem like he will be helpful this time.

In terms of chapters, I don't know.