Adding a Control Track
Is exactly the same as adding other tracks into Timeline, right click in the editor window → Control Track.
Changing Time Elements of a Game Object
I have gone ahead and dragged a game object into the Control Track (as seen below):
Now, within the Inspector window, you can see that it has allowed us to adjust the time-related elements of this game object:
Control of Additional PlayableDirector
I have also gone ahead and created a second PlayableDirector onto another empty game object and then dragged this game object onto the Control Track:
What this allows us to do is essentially have nested Timeline sequences within each other allowing for complex cutscenes that can be managed and controlled quite simply by utilising a Timeline Manager.