The basic problem, as I explained before, is that you cannot replace or remove the transition, which your newest example still does, or the transition animation will break. You are literally replacing or removing the property that is anchoring the animation; that you're replacing it with another transition property does not matter.
Your original post made it sound like you were adding content via the <<timed>>, which you then wanted to fade. And there was the hover bit, which made it seem you were really doing something more involved that you let on.
If you're just attempting to get something to fade in and then out after some period, then what should trigger the fade in and what's the hover bit for? It would really help if you explained exactly what you want to happen at every stage.
Regardless. If all you need is a fade in and then out, then the following will CSS work:
transition: 4s opacity ease;
With the following markup:
<<addclass ".seeable" "see">>
<<removeclass ".seeable" "see">>
Note how I do not remove the class containing the transition, rather only adding and removing the class that alters the property that is being transitioned (opacity).
I doubt I'm on target just yet, but that should be closer to the mark.
EDIT: Fixed a bit of reading comprehension failure on my part.