I don't know the time spent. I did see his home workshop which was very large and well equiped. He had a very sophisticated lathe which he used to machine the ship's hulls. His models were made out of hardwood, though he did experiment with resin. But resins back then were not as good as they are now.

He also used plastic sheets etc. This NATORI Class model has a plastic hull, as well as other parts scratchbuilt from plastic. It was made decades before Neptun produced a model of comparable quality.