Length limits come from how the underlying AI video models work, they generate one scene at a time:
- Single clips (UGC, UGC Hook, Product Animation, …), up to 15 seconds each.
- Full video ads (Commercial / Idea), multiple scenes stitched automatically, typically around 20 seconds total.
- Longer videos, generate several clips, then combine them yourself: go to Library → Video Clips, select the clips, and click Video Editor. You can order scenes, add a voiceover, and export a longer cut. See Combining clips in the Video Editor.
For paid social ads this is rarely a limitation, 15–30 seconds is the sweet spot for Meta and TikTok ad performance, and shorter hooks usually outperform long cuts.