29 hours for a frame is high but not unusual. Referred to as "Blinn's Law", the tendency is that scene assets grow with computing power, eating up any performance gains that you may have gained from newer hardware. Render time for an animated movie today is still in the same order of magnitude as it was in 1995, using state of the art hardware.
Now, how can they do that at 25fps all of a sudden? They're not. They're using the same method, but not even remotely the same scene complexity or image fidelity. Ray tracing, and its extension path tracing, scales very well. The same algorithm that works for 500 polygons works for 500 million polygons, as long as you can fit them in memory - it's just going to be slower (building quality acceleration structures is often O(n log(n)). If 10 rays per pixel don't give you the quality you want, you can go up to 100 or 1000 rays per pixel, with render time going up respectively.
For film, we're rendering hundreds of primary rays per pixel (tens of secondary rays for each primary ray), with hundreds of millions of polygons per scene. I have no insight about the scene of Nvidia's demo, but it is claimed to run at 5 rays per pixel. So even if scenes were identical, it's already 20-500 times faster just by doing 20-500 times less work.
Shading complexity is also a huge difference. Production rendering uses tens of GBs up to the TB range just for textures, on top of procedural shading. Not only does the computing part of that often dominate render times (instead of the ray tracing part), but just paging texture data in and out of memory on demand can become a bottleneck by itself.
That Nvidia demo is a simple scene with no I/O overhead, rendered using a fraction of the rays used for film production, on 18 billion transistors of specialised hardware. Of course it's several orders of magnitudes faster, how could it not be?