It takes anywhere form an hour to 2 I believe. I played half of the game and lost interest once I got to the third level. By the way, Journey was my GOTY for downlable games excluding The Walking Dead seeing I got that on disk.
My little brother beat it on one sit in and he's 13 so I guess that should be enough info I hope for you.
It is longer than Journey for sure. I did not finish it in one setting. It is a good game. They just had it on sale a few weeks ago. Too bad you missed that. Warp is another good game, but I haven't finished that one, so I don't know how long it is. I would say The Unfinished Swan too me about 1.5-2 hours, maybe a bit longer. I am guessing you played the demo. If you liked the demo, you will love the full game. I love it's artstyle. Very unique game.