If you double click on the object it opens it in the Edit image window. In the Animations window that also opens up select the animation you want to set the speed for. Once you have selected the animation you can set the speed in the Properties window. (It's the main Properties window, there isn't a special Animations Property window.)
FYI: If you right click on the animation in the Animations window you can select Preview and get an idea what the animation will look like.