I’ve given you the answer so there is no use in pursuing this further.
You don’t seem to understand what is happening. The curtains close taking 11.3 seconds to finish ( 8 seconds duration and a wait of 3.3s before they start).
If you then fade out outer at 11.3 then you will see a flicker as outer starts to fade.
You need to hide the stuff under the curtain while the curtain is closed and then you can fade in the buttons without seeing anything that you don’t want to see. I gave you code for that.