You won't know until you take gravity readings with a hydrometer. Test your beer, and if the gravity stops falling/remains consistent for 2-3 days, it's done. There's nothing wrong with letting the beer sit for 2-3 weeks in the primary on your yeast cake. I like doing that with almost all of my beers as the yeasts will continue to clean up any fusel alcohols and diacetyl that might have been created by a fast ferment.
My Scotch wee heavy sits for two weeks in my primary before i'll touch it. Then, I open it up and toss in about an ounce of single malt scotch infused oak chips and let those stew in it another week before i'm ready to rack to the bottling bucket.
Beer so good, it's frightening.
2014: Seven Heavens Series One: Vilon, Mystic Melomel, Skeeter Pee.