The RepeatBehaviour property allows you to specify how long the animation will repeat.
You can do this either as a TimeSpan or you can choose to specify Forever.
If you specify Forever, funnily enough it repeats the animation and carries on repeating it.
If however you specify a TimeSpan, you can choose a multiple of the duration or a fraction.
In the following example, the top ball repeats 1 and a half times and the bottom one forever: