visability on an objects shape node (the one you see in the channels) is a boolean and usually not animated and is more accurately the display of the object rather than how visable it is. when it is off the objects shape will litterally not be in the scene.

If you want a fade it is done using the matterial, simply keyframe the transparency of a matterial over time along with any reflective attributes may still cause it to be visalbe e.g. specular color.