Imo highly individual. In my practice, I've observed inflammation in my heel decrease in scale of a few weeks (my heel used to be inflamed after every run for a few days, with me unable to recover from 2 weekly runs of ~ 6km; after 2-3 week started to improve, now - 2 mo later - it is completely healed, can run 4-5 times a week, and bottleneck is now something else). The second effect I observe is my decreased fear of cold shower & improved ability to handle it (both psychologically and physically).