Mmmm, I played the preview copy of the game (which contains three of the six chapters) for a Dutch gaming website, and it took me about six hours to complete it (only the first half of the game). I think it is possible to finish the complete game in 7-8 hours, but only when you play it on the easiest difficulty and you’ve already played a large section of the game before.
You aren't familiar with the Ship Simulator series? Tshhhh! :P