This is due to technical reasons. Trimming is possible only at fixed 1 second intervals within a clip.
- How can I expand my stories in the main timeline of Storyteller?
- How are the Story images sorted in a Story video or online sharing?
- How do I export a cinemagraph as a .gif file on my Lumia?
- Why are not cinemagraphs stored as .gif by default on my Lumia?
- Why should I use Storyteller instead of the Photos app on my Lumia phone?