Actually it has been stated that this game is not so long, but more dense like Majoras Mask.
So I have to guess about 20-25 hours, 30 max.
Now 100%, like in Majoras Mask, it takes some more time, so 100% in a first run I would dare to say 25-35 hours top.
actually how long the game last depends on the player. everyone does things at their own pace. and this game has recently been said that it's the largest zelda game to date. to me that means that it will probably be longer than most because of all the content. i don't do 100% completions. i never have for any game. and usually it takes me 5o hours or so to complete a zelda game. i'm talking about console games not handhelds since i've never played any of those. that's on a first run.