A rule set that is unique to oneself is similar to a True God's Godhood and is one of the prerequisites necessary to become an Ancestor, after all, the powers wielded by an Ancestor are sublimated from the rules unique to oneself.
Although Lin Xiao now masters the Time Law, he only possesses fifty percent of it. Unless he can fully master all of the Time Law, it's impossible to use it as his unique rule, preventing him from using it to ascend to Ancestry.
Reviewing the rules he currently masters—time, matter, balance, creation, truth, life, magic, black hole, reincarnation, as well as the Dream Law obtained from his wife, Tishar.
Among them, time and matter are incomplete, definitely unable to be used for ascending to Ancestry.
Magic does not exist in the Wizard World, making it impossible to be used for ascension to Ancestry as well.