So that he can train Harvey Dent, for instance.
Is this a problem? No, not really. Bruce Wayne is an extremely wealthy man who can afford to buy "plane tickets". He can use these to fly from where his boat docks to Gotham, where he can hang out for a while, before using the "return" portion of the ticket to rejoin the boat.
I'm sure that if anything interesting happens during his year off, and which isn't covered in 52, then Batman or Detective will cover it as a flashback after 52 finishes.