I'm trying to figure this out, and not having any luck.
Under System | Preferences | Power Management
The Power Management Preferences dialog has a tab for 'On AC Power' and 'On Battery Power'.
Each of those tabs has a checkbox marked 'Dim Display when Idle'.
If I check that checkbox, the display dims after exactly 40 seconds of inactivity. It doesn't care what I have the screen saver's "Regard the Computer as Idle when Inactive For" slider set to, it doesn't care what I have the Power Manager's "Put Display to Sleep when Inactive For" slider set to.
Can anyone shed some light on where this 40-second time-out is coming from and how I can control it?