My wallpaper is updated even at night, although I have set visibility span to -4/+4. Can you please fix that?

Visibility span settings actually filters those webcam that are located in a selected time span, related to your timezone.
Example: if you are located in GMT timezone and you set timezone span of 0, you will see only webcams that are located in GMT. This setting affects only popular and random lists in Worldscope WIdgets, not in the main app (Worldscope Webcam).