Fang Ming's timely arrival was due to the efforts of Fang Qing and Zeng Yifan.
After Fang Qing was thrown out of the Dragon Soul office by Stone Sword Edge, she quickly called her father, Fang Zhenhai, pleading for him to step in and rescue Su Chengyu.
Fang Zhenhai, in his high status, naturally couldn't intervene on behalf of a nobody like Su Chengyu to interfere with the Dragon Soul office's operations. However, due to Fang Qing's relentless entreaties, and even the lie that she was carrying Su Chengyu's child, he conceded.
Fang Zhenhai, though, was angry, but he eventually agreed due to his love for his cherished daughter.
Fang Qing worried that even with Fang Zhenhai's intervention, Su Chengyu could still be held and oppressed by Stone Sword Edge in the Lin Jiang Dragon Soul office. To ensure his safety, she also called her older brother, Fang Ming, asking him to hurry over.