C490 Tai Qing Jin Dan
When Yang Feng first formed his core, he was at the back mountain of the Tianjing University in China, on Earth, and had to use all the spiritual energy of the dragon vein to form his golden core. From the time he started cultivating there to the time he formed his core, it only took him three months.
However, to be able to reach the Core Formation stage within half a year's time