A very long time due to constantly remaking the mesh and parts of it to be more accurate & whenever better sources appeared ( before pokedex 3d pro came out my only decent reference from all angles was a rip of the Pokemon Colosseum model which is incredibly inaccurate for an official product and a grainy picture of two anime character sheets )
I don't know how long it would take me to remake a model from scratch now depending on complexity but I want to learn ZBrush to have more flexibility in scaling the triangle count and making normal maps.
Most of it is working on top of a Turbosmoothed result of a lower poly base I did so I think it's around just over 20k. Which I'd say is acceptable for the player character models if you're using a machine that could reasonably compare to a ps3 or xbox 360, but I haven't done extensive testing with how well Unity's renderer performs.
How many polys was that model you posted in the screenshot showcase? Looks phenomenal. I was working with low poly models a while back and had thoughts of working with a Unity Engine, but it was really me just kicking rocks in the sand.