I'm listening to an audio book right now - I can select any chapter I want and it shows the chapter length fine. This has been working the second I upgraded to iOS7 the day it was released.
See, for example, these support thread with hundreds of comments: https://discussions.apple.com/message/16397272#16397272
The sad thing is that they don't give 3rd parties access to m4b metadata (chapter name, length and cover), and they themselves have broken their Music.app's ability to parse them. So nobody else can fix this mess.