Not going go into too much details because it's a huge spoiler, but basically there is a timeline inconsistency in this part that is needed to support a new plot twist. Eric, go look at the part when they say 'this event took 20 (I think?) months to happen", and then check the relevent timeline. The only way the events could have happened is by defining that event to take 20 months instead of its usual time, except in doing this it's basically like saying the event took 1 Jedi year which is really like 2 years.
People on the boards have the official timeline mapped with information from the offical sourcebooks. No matter how you slice it the events in this part could not have happened, because you're short by one year and that'd violate casuality. So what Oda is saying that you can't even trust time to be a consistent unit of measure in OP. So when they say some ancient civilization vanished 1000 years ago maybe it really means yesterday. Given the relevent timeline is established way back at around volume 10, I really doubt Oda ever planned anything. It's more like he suddenly had a great idea and someone told him there's no way this timeline could work but he just ignored them anyway.