How long does it take to build a 3D-printed house?

Alquist used a massive 3D printer to create the structure of the home out of concrete, rather than wood and other traditional materials. The process took just 28 hours — the typical Habitat for Humanity house takes at least four weeks to construct — and it cut building costs by 15% per square foot.

I wonder if in the future they could use a concrete which included hemp? I've seen some really good info about hemp as a building material.