If you want to adjust the duration of an image/ video clip you can do this two ways:
1. In the timeline drag the border of the image/video-object further to the right side, if you want to increase the duration and to the left to decrease the duration.
2. You could also use the „Properties“ toolbox and enter the exact amount of time under „Duration“. You can create a time lapse by speeding up the play back speed or slow motion clip by slowing the playback speed, both adjustable in the properties toolbox.
Note: In SlideShow 9 you can’t change the speed of a video, but you can cut the end in the same way as you would change the duration of an image. For adjusting video in SlideShow 10 please see this video.