Remember, brevity is the soul. Click 'Automatically after' in PowerPoint's Slide Transition task pane, and set a time for your slides to run automatically.

Learn how to make or create a Countdown Timer in PowerPoint. You can also use an Add-in. Displaying a countdown timer in your PPT can be helpful in many ways.

You can add Slide Numbers and Date and Time to your PowerPoint presentation to make it more impressive, and this post shows how to do that.