Lock Screen after screensaver starts + delay

Set your screen saver to lock when it comes on, then open regedit.exe to

HKey_Local_Machine\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\

Find the entry on the right hand side of the screen for ScreenSaverGracePeriod (if it's not there, create it as a REG_SZ. Add (or change) the value to be 600 (that's 600 seconds, or 10 minutes).

Now, your screen saver will come on at 5 minutes, and you have an additional 10 minutes past that to wiggle your mouse and come back. After the screen saver has been on form 10 minutes the computer will automatically lock itself.

It may be obvious to others but after testing I had to check the box to display log on screen in Screen Saver Settings window to get it to work correctly.