im still reading the novel and im only a bit more than halfway but a bit of a spoiler to understand the plot....
there will still be more info than this so this isnt exactly a huge spoiler but to better understand the worlds!!!!!
first world: apocalypse happened and lee sayoung died. cha euijae turned back time by becoming the pivot/axis using the watch created by hong yesung and he was successful.
second world: cha euijae died this time and lee sayoung found out that there was an "error" with the watch created, it was supposed to be a one time use only but cha euijae was too strong that it left some power so lee sayoung was able to turn back time as well by becoming the pivot/axis this time.
third world: current world where both of them are still alive and this is their last chance to save the world.
when they reset time, a new world exists and the old one becomes deserted so the last two worlds shouldve been destroyed but the west sea rift was an anomaly in the third world that showed up and it looked exactly like the destroyed worlds. due to the multiple resets, the other worlds clashed with the third one, causing confusion with timeline and memories, not only for the awakeneds, but even civilians. on the upcoming chapters, they will start to explain the difference between the first two worlds with gaeul. the reason why it's their last chance is because the watch only has three clocks (?) and only the last small clock is moving, which represents their world.

Im lowkey confused ab the plot like I genuinely want to understand it so someone please send help, i get it somewhat