You can set a presentation to play continuously in a loop and to restart if it sits idle for a specific period of time.
Restarting an idle presentation automatically is especially useful in a kiosk setting. If a presentation is playing and there hasn’t been any interaction with the screen after a period of time, you can have the presentation return to the first slide.
By default, when you reach the last slide of your presentation, the presentation ends and Keynote returns to editing view. Instead, you can make the presentation loop, so that it returns to the first slide when it reaches the end. You must set up your presentation to loop before you begin to play it.
Tap 
, then tap Presentation Tools.
Tap Presentation Type, then turn on Loop Presentation.
If a presentation is playing and there hasn’t been any interaction with the screen after a period of time, you can have the presentation return to the first slide.
Tap , then tap Presentation Tools.
Tap Presentation Type, then turn on Restart Show if Idle.
Drag the slider to set the amount of idle time before a presentation restarts.