It's hard to give an exact time as it depends on the manga's plot development. But typically, Yuta Okkotsu shows up when certain events and character arcs lead to his introduction.
The following are the recommendations of a few anime master apprentice novels: " Raising a Disciple to Cultivate ": This was a classical Xianxia novel, which told the story of a master and his cute disciple on the path of cultivation. 2. [My Apprentice Is Very Arrogant]: This novel tells the story of an evil master and his arrogant apprentice. These novels all have plots about anime masters and apprentices, which can meet your needs.