Well, I believe the 3D2Y is set in piece.
It seems alot of time since One Piece is always evolving and we do not take notes of days... but it is a reasonable time for the training they are facing, starting with luffy and ending with whoever. They have not easy tasks, 2 Days aren't enough, 2 weeks or 2 months neither.

Oda isn't the kinda of timeskip writer, but he isn't a training arc either. He did no one in 600 chapters, he will not start now, i wouldn't want it atleast.

There is nice theories here, but are nothing more than theories. Did he mourned Ace or SH? I don't think he was mourning a SH dead, since they aren't dead and they are suppossed (and will) be together again as Strawhats, although I believe the 16 bells were directed at them, to signify a new stage.

Well we will get 1-2 more chapters before we have a confirmation of what Oda will do next.