Around 11 AM - 11:59 PM Daily (with two 'one hour' breaks for lunch and dinner respectively), so that's around 11-12 hours.
Well, almost 10+ Hours...! When ever am awake, Computer is ON.. even when i eat, Or Bath Or whatever, It is ON . Some days my computer works for 18+ hours... some days i keep my computer on the whole night so i can have some downloads finished by morning