That tileset is a lot smaller than it looks in Cyangmou's post. All the the daytime variants can be discounted, that is at best 30 minutes of work as it is nothing but palette swaps which do not take long with decent software, esp if the artist is experienced. First of there are a lot of dupes in this tileset.
Then there are a lot of tiles which are essentially the same just with a different colour as well, like the roads. The snow and grass base tile are the same, just different colours and slightly different offset of the pattern, so just copy pasting a bunch of roads or rocks around and then adjusting the palette where it needs to be adjusted (shadows/aa) does not take long either. Same goes for the coastlines, the mountains, a whole bunch of the buildings and so on.
I think that an experienced artist who knows what will be needed and has some technical understanding as well as close communication with the programmer will be able to do this in 1 or 2 days.