Assuming your slides to the Bar Mitzvah Montage contain 2-8 images per each slide, you might want to suspend all on-screen slide around 5-30 seconds (depending on your chosen format) in order to draw attention to the optimum.
The more you use one slide images – you’ll have to extend the time to last screen to see.
The more you use less transparency and information – you’ll have to reduce screen time so as not to bore the audience.