This is very strange. Dragging plugins into Blender from this page doesn't work, but searching for and installing the plugin in Blender's preferences makes it effective.

This is a great Add-on that definitely should be a native blender feature. However, limiting the add-on to just the 5 editors it currently supports is arbitrary. I wish this was a toggle on the side of the editor bar and I could open this ANYWHERE. Shader editor, Geometry Nodes Editor, the bottom of the properties' menu. This would be most useful in editors that have nothing to do with animation in the first place, so we don't need to cram the UI with 200 editors on top of each other.

exactly what it says, handy for those of us trying to 'convert' to the dopesheet after using the timeline editor. I really want to have the ability to toggle it off on certain editors, because I don't need it on both my graph editor AND my dopesheet timeline.