Setting the timing of automatic slide changes
You can set up a slide show to run automatically, either unattended or while you speak. To set the default time for slides to be displayed before changing to the next slide, go to the Slide Transition pane, leave the transition effect set to No Transition, choose Automatically after in the Advance slide section, set a time, and click the Apply to All Slides button.
To vary the times for some slides, choose Slide Show > Rehearse Timings from the menu bar, or click the Rehearse Timings icon on the Slide Show toolbar. The slide show begins in full-screen mode, and a timer appears in the lower left-hand corner of the screen.
When you want to advance to the next slide, click the timer. To keep the default setting for this slide, click the slide, not the timer. Continue for all slides in your presentation. Impress records the display time for each slide. Save your presentation. When you next look at the time set under Automatically after, you will see that the times have changed to match what you set when rehearsing.
If you want the whole presentation to auto-repeat, open the menu Slide Show > Slide Show Settings. Click Auto and OK.