I was on a server by plornt that did it, but i think it completely remade the sky and sun.
Yes, Plornt has it, and I have his. I used one of his functions and re-created it. Its very simple actually. I cannot tell you how to mod RP Time, but I can tell you a few things.
1: The skybox cannot change. Actually, it can. But I wouldn't suggest it. I have seen scripts change it. It can crash some people, as it sometimes crashes me.
2: Since changing the skybox is very hard, you would have to use Destruct. Destruct is all black, so you won't notice the non-changing skybox. Also, interiors will NOT change. They will stay bright, and their shadows will not disappear... even at night, they will have shadows. This is because they need to be relighted. This can be done, BUT it will normally cause a 15 second lag spike. Also, a very bad idea.