Comment 15 for bug 289322

Dimming the screen turns the backlight down, and blanking turns the screen off, which happens a set time after the screen has been dimmed.

I think I understand what you mean in that: Although the "put display to sleep after" is set to 1 min, even without keyboard or mouse activity it takes a minute or 2 longer.

I think the problem seems to lie in the fact that the blanking timer counts AFTER the screen dims, which doesn't seem correct if the settings say "Put display to sleep when inactive for:", so I see what you mean. Will ask around on this one as it is a little puzzling.