When you select the Fades, Rotation, Scales or Special Effects category in the Animation Wizard, the third page of the wizard will display a list of animation options you can choose from, and control options to set the number of seconds the animation will take to complete.
Click on one of the animation options in the left hand panel of the page.
Use the spin buttons beside the Duration box to set the number of seconds the animation will play for before it stops.
Click on the Next button to go to the final page of the Animation Wizard.
Click on the Finish button to save your changes and close the Animation Wizard.