The Time function in OpenShot considers the entire clip, not just the portion you want to use. To work around this issue, you can export the part of the clip that you want the speed adjusted to a separate video file. 

  1. Create a new project and import only the clip to be adjusted. 
  2. Change the speed of that clip, then export it as another video file. 
  3. Import the recently modified clip to your original project and add it to the timeline.