Yes you should always set a maximum record time when using "always on" mode, just in case there is too much background sound which would cause the app to keep recording forever without actually stopping to analyze the audio file. I keep mine at 16 seconds, because most voice command are going to be less than 10 seconds long, even if you want to string two together.
The error you are getting is a generic Android "Sorry AppName has stopped responding". This happens from time to time with many of the apps that I use and I generally attribute it to the Android OS but I will check the developer logs in case you submitted a report to see if there is actually any useful info in there -- which I doubt.
My guess is that at some point VW is asking for access to the microphone and for some reason Android is dropping the ball, or something along those lines. If the problem was in my code I doubt that it would take up to 24 hours for it to manifest itself.
