When you turn on password protection of a screen saver, it is not effective immediately. There is a 5 second delay by default between the time that the screen saver locks the computer and the time that the password protection is established. During this screen saver grace period interval, you can use a key press or mouse movement to unlock the computer without having to type the password. This screen saver grace period is designed to minimize the disruption that results when the screen saver starts while the user is working.
This tutorial will show you how to change the screen saver grace period to how many seconds you want for all users in XP, Vista, Windows 7, Windows 8, and Windows 10.