LibreOffice assists you in defining the right rehearse timings for automatic slide changes.
Prepare the slides, start the show using a special icon, tell your imaginary audience what you want to tell for the first slide, then advance to the next slide and so on. LibreOffice records the display time for each slide, so the next time that you play the show with automatic slide changes, the timing will be as recorded.
Open a presentation, and switch to Slide Sorter view.
Start the show with the Rehearse Timings icon in the Slide View bar. You will see the first slide, and a timer in the bottom corner.
When it's time to advance to the next slide, click the timer. To keep the default setting for this slide, click the slide, but not the timer. Continue for all slides in your presentation.
LibreOffice has recorded the display time for each slide. Save your presentation.
If you want the whole presentation to auto-repeat, open the menu Slide Show - Slide Show Settings. Click Loop and repeat after and OK.