I'm watching ep 1 again. I noticed that the late King said to Jang Kang, they'll soul-shift for seven days. After…
Time-limit? There's no such thing as it. Remember Jang Kang (in late King body) asked Jin Mu for help, so he can change it back. It makes Jin Mu get to learn about AoS and ice stones. Not sure about "return" part.
Not sure about "return" part.