Presentations
Google Slide - - Under Google Embeds >>Slides
The presentation must be shared. I have this one set to Public on the Web. You can select to auto start, loop playback and change the delay time. I think these options are new. Click the slide then click the settings icon (gear).
Note that on a mobile device the presentation will not auto-start. The viewer must click on the presentation to bring it up and then click the play icon.