No I am not talking about the screen locking and preventing viewing and changes without a password. This of course like you say is a great security feature. This has a timeout of 10 minutes. So after 10 minutes of inactivity it goes to the home screen and locks the keyboard.
I am talking about the screen dimming to a barely visible dark grey, from a nice a visible yellow. This has a timeout of exactly one minute (far too low). Also when the screen dims it does not lock the screen! So it is in no way a security feature.
I hope this is clear now.