Yeah his quality since Miriam 1 is a significant increase, I'm unsure what programs he uses exactly, but I know most 3D Rendering programs allow you to literally replace a model for another have it in the exact same position without ruining the structure or having to recreate the position, scene or lost any amount of work.
Rendering takes a hell of a lot of time, to put into perspective, ILM used 200,000 rendering hours per day to render Transformers: Dark of the Moon, that's the equivalent of almost 23 years of rendering per day.
So going by what content BA makes, I can imagine it taking a good week or two combined, to render every image in a set from start to finish (assuming each image is rendered perfectly with no flaws, like clipping, or texture or lighting errors)
TL;DR - Shit takes time to make, and that's not including storyboarding and actually setting up scenes, Takes even longer if you have a shit rig.