I've also had problems with the timeline after upgrading to V8, the Light Scene would take longer to run than the song to finish. It worked fine in V7. I've timed the Light Scene in Steps (where I created it) and ran a timer on my phone. The 4 min Light Scene, in ShowXpress would time out at 4 mins. On my phone it showed 4:15.
I was wondering if anybody else could run a external timer on their Light Scenes to see if they are having the same issue. This might be the cause of the Timeline issues. Just a thought.