Holy cow, I wrote a book!
You may find yourself in a situation where Windows takes longer
than your specified screen saver idle timeout to start the screen saver.
First of all, there are ways for programs to block the screen saver
is how a program says,
"Even though there is no mouse or keyboard input,
the screen is indeed in use, so don't blank it or start the screen saver."
Media playback programs use this so the screen saver doesn't kick in
while you're watching a movie on your DVD,
and presentation programs use it so the screen saver doesn't start
in the middle of your multi-million-dollar proposal.
But even if no program has marked the screen as busy,
Windows itself will delay activating the screen saver if it detects that
you would prefer that it not run for a while.
If you repeatedly
dismiss the screen saver less than one minute after it starts
on Windows Vista or later,
the operating system says,
I thought there was nobody there, but obviously there is.
You're probably reading an information-dense document or
using your laptop as a flashlight
and you want the screen to stay on
even though you aren't generating any input.
I'll hold off the screen saver for a little while for you."
After the second time you do a
"fast dismiss" of the screen saver,
the screen saver idle time is temporarily incremented by
its nominal value.
For example, if you set your screen saver timeout to two minutes,
then starting with the second fast dismiss,
Windows will wait an additional two minutes before trying the
screen saver again.
Here's a timeline for people who like timelines:
As long as you keep fast-dismissing, the delay will increase.
Of course, the delay won't grow indefinitely, because you'll eventually
hit some other idle timeout, like the system sleep timeout,
and then the system will sleep before it gets a chance to run the
If this feature offends you, then you can disable it by
setting Adaptive Display to off in the Advanced Power Settings.
There are also
Group Policies for controlling this feature.