Nutrient absorption does not take long at all. The problem is when food hangs out too long in our digestive tracts where it becomes a problem. It ferments/rots and causes odor, improper flora balance, and toxic overload. There are people that only poop once a week! 3 meals times 7 days is 21 meals backed up in their guts!
The body knows what it is doing with food. It absorbs what it can of a particular food and moves it along once it is done. You never will absorb 100%. Watermelon passing through you in 11 hours? No big deal. That's what your body decided to do with the watermelon.