I think the 20 minute timer should be visible even when the clan castle is full. The reason why this would help is because some people (like me) request for troops right after an attack, then go offline so the troops can be used for the next attack or sometimes a defense. Without the timer, I don't know when I last requested and sometimes finish an attack to find out that I have to wait a few minutes until I can request, and I have better things to do than to stare at my empty clan castle, and if I closed the game, I might get attacked with no clan castle defense.

