1 to 2 days is needed for those who really wish to explore all those earth houses. And they are situated in the mountain. In order to reach them, you must get there as early as possible.
Hakkanese earth houses are different with Hokkien eat houses. Which you can see here, it is a earth houses made by Hakkanese, interiorly made by ceramics.
Actually there are few hundreds of this kind of earth houses around the area, do your research 1st before you go, the most famous and most visited is Nanjing Tulou and Yong Ding Tulou, others also open to public.