Using a Timeline to activate objects

We just added an Audio Track to the Timeline. Another type of Timeline track is an Activation Track. Associated with a specific game object, an Activation Track with enable or disable that game object at the specified times.

According to our plan, when the timeline starts, the bird's nest will be hidden (NestAndEgg object). At the 35-second mark, it becomes enabled. Also, when the nest is first enabled, it should have the WholeEgg. Then at the 80-second mark, it is hidden and the HatchedEgg is enabled instead.

The NestAndEgg game object hierarchy, as shown here, contains the Nest itself, a WholeEgg object, and a HatchedEgg (which has the two eggshell halves):

Let's add the activation sequence to the Timeline now:

1. With BlackbirdDirector selected in Hierarchy, drag the NestAndEgg object from Hierarchy into the Timeline Editor window.
2. A menu pops up, asking what type of track to add; choose Activation Track.
3. A small rectangular track marker is added to the track...