I could be wrong but I think “Exposition” is a type of event that only exists in Narrative View, so it can’t be added to Timeline View and its purpose is help you plot your Narrative timeline.
The name is bit misleading, though. I’m using the Screenplay template and I renamed “Exposition” to “Story Element” which makes a little more sense to me.
I’m still not entirely sure, though, what the difference is between “Exposition” and “Narrative Folder” since both can be used the same way; that is, you can put other events inside an “Exposition” event just as you can with a “Narrative Folder.” Maybe someone else can clarify the differences.