The menu is opening like it should for the registry setting for the delay. The reason it is opening slower than the others has to do with what is inside those folders.
When you mouse over it, it is looping through the folder contents to pull what is in there, the icons and so on. Just the same way when you go open a folder. Depending what is in there determines how long it takes to open. This is because it is reading each file, to pull its icon, size and what ever other info it pulls.
So to test that, try removing some of the files, all the big ones, or any that dont have a proper icon. That one alone could be what is slowing it down since it shows that windows had trouble loading the icon for it, so it took a bit more to load.
Shane