User blog comment:AldenHeathcliffe/Chapter 551: The Burnt Offerings/@comment-10630156-20131003080937/@comment-6657474-20131007014618

Kyoraku was able to return quickly after the Wandenreich started their second invasion, so it's safe to assume that Isshin, Yoruichi or others could get there fairly quickly as well. Don't forget that Yoruichi was able to travel back and forth between the human world and the Soul Society an unknown number of times after being exiled. Also since captains are often sent on missions in unknown and hostile territory, being able to navigate the unknown quickly would almost surely be a must-have skill (with Kenpachi Zaraki possibly being the only known exception), so finding their way to their allies in the Schatten Bereich shouldn't be a whole lot of trouble for them.