Slideshow duration on a large presentation

Yes, a large slideshow with many slides, high-resolution images, or animations can affect the duration reduction. Longer transitions or animations may slow things down, and the file size can impact performance on less powerful devices. To reduce duration:

1. Shorten Transitions/Animations: Use faster transitions or eliminate non-essential animations.
2. Batch Edit Slide Timings: Set uniform timing for all slides (e.g., 2 seconds per slide) in slideshow settings.
3. Optimize Content: Compress images or remove unnecessary slides to improve performance.

You don't mention if you are using a Mac or an iPhone or an iPad.

On a Mac, the Photos Slideshow Project offers control of overall timing:

There's a minimum, of course, but this 70 picture slide show could be set as high as 33 minutes duration, although that depends on the speed of the transitions, which you can also adjust.