You need to place your time keyframes at different times in the replay, otherwise the mod will have no idea when in the replay the path is supposed to start and when it's supposed to end.
1. Jump to when you want your path to start
2. Place first time keyframe at 0:00 on the bottom timeline
3. Jump/play replay to when you want your path to end
4. Place second time keyframe at however long you want your video to be (you can also press V to automatically move the cursor to where it needs to be depending on the Replay Speed slider)