Play animation is controlled by the controls at the bottom of the play diagram.  The buttons to the left control the flow of the play and the slider to the right controls the play speed.
The play button starts/restarts the play animation, the pause button pauses/unpauses the animation, and the reset button cancel the animation and restores the playart for the play.

The play speed slider:
controls the speed of the animation – moving the slider to the right increases the play speed while moving it to the left decreases play speed.