The Wu Sect's action was fairly swift among the sects on the continent; they began the construction work thirty years ago. Over time, the building complex began to take shape, and, in recent years, is now recognizable enough for occupancy.
It's impossible to wait for everything to be complete before relocating because construction will never stop. Once the main works had a rough outline, everyone moved in and began to add to it slowly, as needed. To truly build it into the likeness of an Immortal Mountain would take hundreds of years to accomplish.
This included the transformation of the Five Elements, the establishment of the Mountain Gate Formation, and even the rearing of spiritual beasts and immortal fowls, among various functional palaces—just too many things to list.
