Depends on how often you play the game, and how good you are at beating the tougher fights quickly. Took me 16 months with a final in-game time of 344 hours, though I was also recording most of my gameplay to show my family, narrating every word of the story and doing a lot of random exploration. You could probably do it much faster if you read the dialogue quickly and are good at the game.
I should note that I'm already at 40 hours played on Reborn E19 and I'm only at Apophyll, so it might just be a me thing.