How fast can colon polyps grow?

Relatively : Slowly. Usually from a single cell to a polyps the size of a pencil eraser takes 2-3 years, but there can be a wide degree of variability in both benign and malignant polyps.

Usually slowly: Polyps generally grow slowly, taking years to get big enough to be visible. However, there do seem to be some that are faster growing and more aggressive. I have certainly seen them show up in less than a year after a previous colonoscopy.

Varies: But tend to grow slowly & that is why colonoscopy surveillance is recommended every 5 years with risks or every 10 years if no colon cancer risk factors.