AI, which isn't always 100% accurate, offers this. Give it a try...
"In NCH PhotoStage, you can determine the duration and the number of photos in your slideshow using the following steps:
Viewing Slideshow Duration
Sequence Preview Area: The total duration of your slideshow is displayed in the sequence preview area. You can also control playback here to review your slideshow progress.
Adjusting Slide Duration: To view or change the duration of individual slides, click on the time displayed below each slide in the sequence area. You can enter a new duration in seconds and save it.
Counting Photos
Media List: The Media List area shows all images and videos added to your project. Each file in this list represents a slide.
Sequence Area: The sequence area displays all slides added to the slideshow. You can count them directly or use sorting tools to organize them.
By reviewing these areas, you can easily track both the total duration and the number of slides in your project."