I don't use the school restrooms. So..I know I held it for like 9 hours daily. Also, I can usually hold it all day. There have been the few times I challenged myself by drinking a wee bit more fluids than usual, in which case I can last maybe 4-5 tops. I usually go after less than three on those occasions.
In some respects, I held it for 3 weeks. After my back surgery I couldn't go on my own, so I had to learn to catherize myself. So I guess that's like holding it forever. Andysetra, my wife is diabetic so I know where you're coming from. When we used to go on trips, I was forever stopping so she could take bathroom breaks. Aaarrrg!