What’s the Timeline View and why is the Timeline toolbar icon grayed out?
The Timeline view (TLV) is a grid-like display of the Scenes in your story, and is accessible only from the Scenes view. The toolbar icon will be enabled when you click on Scenes view in the Source list.
In the TLV, you can create storylines, assign scenes to storylines, and reposition scenes temporarily to help you develop your story. While the Scenes view allows you to outline your story in the order it will be told, the Timeline view allows you to manage those same scenes in their natural chronological order.