It's more like 24-36 hours, but could vary I guess depending on the person. When I had mine late last year, I could only do clear liquids after midnight the day prior, so I went about 33 hours before the actual procedure. However, I had a recommended diet of foods to avoid for up to 7 days prior. The fun part though, is that nasty prep drink the day before, which varies depending on the person as well. For me, it kept my appetite away, and I'd get a little nauseous at times. There is a temporary perk though, he could lose about 10 pounds or more, depending on how full of tit he is....lol