sun light in DP

This is Darkplaces Engine. And this seems to be dynamic! How they did this?!

I'd be happy with just the smooth transition between day/night skyboxes. How can I get this in DP ? Shaders ?

I did a sun once using shaders and q3bsp and Q3Map2 in DP. But it was not moving.
I also read (don't remember where) about some special shader instructions to move the origin of the sun every second/millisecond/whatever.

Another way would be to manipulate QuakeC, or even CSCQ (not sure) to generate a shader on the fly and apply a slight origin change.

I'd go with the first version if I could find those instructions.