I can not change the duration of the slides

I can not change the duration of the slides. In the previews, I select the photo and, from the properties, I try to change the duration with the arrows. I see it change but when I start the slideshow the duration remains fixed at 00: 00: 02: 11 (the initial duration). I have Shotcut 18.07.02 with Windows 8.1
Also sometimes the sw crashes and I have to restart the computer
Can you help me?

After the photo is in the Timeline, you have to change the duration by dragging the trim handles just like a video clip on the timeline.