Compiz-Config Settings Manager isn't working for Unity 2D because Unity 2D uses Metacity instead of Compiz. You can enable Compiz on Unity 2D using the command compiz --replace in a terminal. After that, you can edit the reveal timeout settings in Compiz Config Settings Manager. However, this will be undone at the next startup. To get Compiz started up by default instead of Metacity in Unity 2D, use this answer and question.