And to think we all complain about compile times of 15 seconds….
But 30 minutes seems insane for ray tracing a single frame. Is there really that much stuff going on in these movies?
They simulate rays of lights bouncing around, so yeah.
Global illumination is fairly expensive (at least the algorithms I looked at back in the day). I would guess a lot of CPU time is spent in shaders as well. And there are all sorts of deformations and what not that need to be applied to the models. And there are a lot of things in each scene.
The wikipedia page on the Reyes algorithm has some interesting information but doesn’t directly answer your question: