oh wait is this dude that orphan did everything just time skip?
I know this is 3 years later, but what happened is that time is weird in the dungeon. It doesn't pass at the same rate, or even the same way, as outside the dungeon. Days inside the dungeon could be months or years.
In my head, I imagine each person having their own personal time line, that gets knotted and looped around other's timelines where it may come in contact in multiple places, but each in in random places of the others.