The time for Lu Li and Jiang Qiling's appointment hadn't come yet.
Jiang Qiling said that in a year and a half the small Demon-slaying Grounds was going to be available. Hence, Lu Li had decided to set off a month earlier. He had just reached the Eternal Realm and didn't even have the time to study his psychic power or to stabilize his situation before he hurried his way to the Central Plains.
If he could not enter the battlefield this time, he will have to wait for another three years - a period of time he could not afford to lose.
Since Lu Li made his deal with Jiang Wuwo, Jiang Qiling had been in closed-door cultivation. She didn't come out even once during this time.
During his four visits to Jiang Yi, Lu Li had asked for Jiang Qiling and was informed that she was in closed-door cultivation. He had gone to her a month in advance in case she had forgotten about it. This way, he could have a window of time to react if it really happened.
