He doesnt really say that he turned back time atleast on what I read in the novel. He just said this to gain equal footing with hyunje, basically he declared this and become hyunjaes "partner" (kinda saucy in the novel) and for hyunjae to treat him as such instead of an item. Then somethings happend and the whole yatch go KABOOM with hyunjaes new skill and suddenly they are in a convinience store eating ramen and riceball.

ok but will yoojin really let his crew know that he "turned back time"?
im up for spoilers pls let me know