Around 3 hours. I take at least 3 - 4 minutes off between sets if it's a small bodypart I'm working on and up to 10 - 12 minutes if its a big, heavy, compound movement like Deadlifts. And I do it on an empty stomach, although I take about 200 mg of caffeine with a strong cup of black coffee about 15 minutes before. I've always trained this way.