Timeline Play Order

I am newbie at C# Scripting.
There is a official tutorial at https://unity3d.com/learn/tutorials/topics/animation/using-timeline-custom-scripts.
My question is if i press left button or right button, Can i switch at timelines order?
For example
if i press left button
index = 1
timeline.Play(1);

if i press left button again
index = 2;
timeline.Play(2);