quincy song

This is quite a freaky question, since as far we all know, so far, Yhwach, aka Juha Bach, is a human. He's still somewhat young/middle aged, and yet, here we are, a whole millennium later, and he's just standing there, lively as ever, as a human... Something isn't adding up. The easy answer...

So from what I understand, 900 years after fight with Yamamoto, Bach got his body back, then 90 years later his memory, then 9 years later his power, and THEN after 9 days he should regain his "World" (basic logic). Now my question: Why did he say that World gonna end in 9 days from now...