In the epiloge of ISSTH Old Man Extermination(OME) says that although he sacrificed everything he had, he has achieved his Dao and in AWE he mentions that he is still trying to achieve his Dao. This means that AWE takes place before other other books. But in AWE it was mentioned that the domain was sealed by Ghost, Devil, God and Demon(3 of the 4 arr the MCs of the other books). This means that either the book takes place after the others or other Ghosts, Devils, Gods and Demons existed before other MCs. If its the former, it crosses with OMEs Dao and if its the latter, Meng Hao mentions that even if Allhaven didn't obstruct their ascension as Immortal, they would still fail because an Immortal already existed. Then if a Ghost, Devil, God, Demon already existed how could MCs ascended as such. Also MCs ascend led as such because they used Allhavens Essence. Does that mean that (if existed) other D,D,G,Gs used the same Essence? Will the plot thicken or am I reading too much into this and this is just a plot hole?
It takes place after. Meng Hao has a cameo in the final chapter. Old Man Extermination is trying to prevent another Allheaven from appearing.
I know this is like 2 years late but for future people looking this up from my understanding a will eternal takes place parallel to the rest because out of all the mcs he reached the peak of the 3rd step the fastest but took the most time to reach the 4th step so he either starts before everyone or between one of the other 3 and then reaches the 4th step after everyone else