Hmm, you should be able to go way longer than that. Seems like a bug.
Or click your scene in the project panel and check the duration in the right properties to see if increasing it shows more of your timeline. Maybe it's being cut off because your duration is too short to begin with?
It may be a bug. I've got the latest cc version of character animator. The scene time was fine but I tried increasing it just in case and I get the same issue. Still the auto lip sync stops right at 5 minutes. I know at one point you announced that one of the updates allowed for an unlimited timeline but from what I can tell, it doesn't work for the auto lip sync.
FYI, This is on a PC and I'm using the latest version of Character Animator.
Ah, I see what the problem is. The default length of a puppet is 5m. Before you run "compute lip sync", extend your puppet clip in time for as long as you expect to need it for your scene.
That's it. I did eventually find the issue myself but was just now getting back to reporting my find but you beat me to the punch. I ended up dragging the clip length to the end of the scene length. Not sure if there's some other way to change the clip length but that worked for me.