Playing Animators Together
If all you need to do is kick off a few animations at the same time, then your job is simple: Call start() on them all at the same time. They will all animate in sync with one another.
For more sophisticated animation choreography, this will not do the trick. For example, to complete the illusion of a sunset, it would be nice to show the sky turning from orange to a midnight blue after the sun goes down.
This can be done by using an AnimatorListener, which tells you when an animation completes. So you could write a listener that waits until the end of the first animation, at which time you can start the second night sky animation. But this is a huge hassle and requires a lot of listeners. It is much easier ...