It's different for everyone. Like the two posters above, the majority of my improvement was immediately after surgery -- within a week I was at my "new normal" of 6 BMs per day. It took about a month for the spasms to die down, and then I had very occasional light incontinence probably through the first two months (e.g. I would wake up in the middle of the night with a dot of liquid on my underwear).
I have continued to notice changes and very subtle improvements over the past ~10 months or so. For example, I did not sleep straight through the night -- ever -- until about four months post-op. Since then the frequency of sleeping through the night has increased very gradually.
Conventional wisdom says that full adaptation of the j-pouch takes a year. Longer term pouchers here will tell you that you will probably notice changes and adaptations for the rest of your life -- for example, it seems like the small intestine's ability to absorb liquid just keeps getting better and better, to the point that many people with older pouches need to take steps to make sure their output is thin enough to comfortably evacuate.
