Can't change the time of day.

When I play on some worlds/places, the time of day settings are faded out and I can't change anything, any help?

 

Not every map has the ability to change time, the ability can be added with World Editor.

 

Its map specific and yes what Godzilla said is accurate as well

 

Alot of mods lack something in the level known as a Time of Day object. This is required in order to change the time of day in the level via the slider in game, or have a day/night cycle.