Day/Night cycle using Keyframes?

Hello guys! I want to do a game with a day/night cycle to my game, with the DirectionalLight and the SkyBox rotating around the world and the AmbientLight changing color using the time. I was already thinking in the maths to do that, when i saw this video. He said he now is using keyframes (0:50).
[video]Java 3D Game Development 32: A Whole New World - YouTube
Someone can explain me how to do that?I already know what keyframes are, because i use them to animate in blender. It would save lots of hours of coding, so can someboby explain me how to do that?

Nobody? Ok, i guess i need to discover by myself…

How about the SkyControl plugin? It would save you a lot of time.

It just took few minutes to implement to an existing project. In this video there are no night/day, but clouds:

I strongly recommend this plugin. Superb!

Thank you so much, this plugin is AWESOME! I just need to learn how to use it, but it should’nt be a problem. Thanks a lot!