The dialog Animation Info is used to create or edit animations. The most important option is the duration, that is given in seconds. At the end of an animation there may be a pause.
More difficult is the value Frames Per Sec. This controls how many pictures are shown per second. This value affects the file size may result in a very large file. When exporting as GIF you should avoid animations covering much space and use a small frame rate.
Repeat Automatically has only an effect, if the animation is exported as GIF, and controls whether the animation is only shown once or multiple times.
The radio-buttons define the condition when to load the destination-URL.
If you don‘t create a new animation but edit an existing one, you can change its length. In this case Existing Animation controls how to deal with the existing sequences. Scale scales the sequences appropriately, Crop leaves the times alone and deletes the sequences, that lie outside the animation.