When a locking screen saver activates, there is a grace period from the time it goes active until the lock is activated.
You can adjust the system wide grace period by navigating to:
Add Value name ScreenSaverGracePeriod as a type REG_SZ and set the string value to the number of seconds of grace that you want. If you are using sslaunch to activate the screen saver, set ScreenSaverGracePeriod to 0.
You must shutdown and restart Windows NT for this change to take effect.