2Dutch --
We can't seem to follow what you are trying to do. Sorry! First, 10 seconds is a pretty short period of time to time-out after a new Page appears. If this has even a small amount of text/instructions on the Page, the viewer will barely have time to read it before the Page starts to fade out. Why would you want it to fade out? Wouldn't it be more effective to have a Text Object start to Bounce (Animation) around on the Page with instructions to "Click Something -- Anything!!!"
Windows XP fades to 50% when you are shutting down. Is that what you want the viewer to think? That you are shutting down?
To answer your questions, just create a Master Page with a Frame covering the entire surface. Give the Frame a gray Background and set it to Initially Hidden with a Show After time of 10 Seconds (or more...). Under Properties - Effects, set the Transparency to 50%. Now set this Master to "Objects from this page to appear on top", and have it be the Master Page for all your other Pages.
If you set the Frame to NOT allow mouse clicks -- then your viewers will NOT be able to make selections -- I don't believe you want to follow that advice. Each time the viewer makes a selection which takes them to another Page, the Frame will reset and start its count-down to fade again.
Please let us know what you are trying to do. I think we can give you better ideas than what you are asking for...
