Windows 8.1 has a new fancy feature called Lock Screen Slideshow which allows you to play a slideshow of images from your pictures library and SkyDrive too when you lock your PC/Tablet. Let's revisit the past for a moment , and you will see that this feature (formerly known as "Picture frame") had many tweakable parameters. Unfortunately, most of them are no longer applicable to Windows 8.1 RTM, however, there is one tweak still available for the Lock Screen.
With this simple tweak you will be able to limit the time for which the slideshow plays.