It was about 15 or so hours to get through things w/ most of the collectibles. It's longer than most games in the genre.
If you want a really quick one that's a good time and doesn't overstay its welcome, try Yohane The Parhelion: Blaze in the Deepblue. I finished everything and got the platinum in that in about 4 or 5 hours.
Prince of Persia is a better game though.