For me it depends what dosage you take. Like I take 25mg XR if I dont drink any liquids it just stays in my system longer. It lasts about 8 to 12 hrs.
I would not recommend not drinking fluids for 8...
generally about 6-8 hours, but I am a big guy I weigh 330 so for someone smaller it would last longer. the less the body mass you have the longer it will work.