It was just a few days for us. I'd think most people would see improvement within say a week? Maybe not all the improvement you're going to get, but some good changes, unless dairy isn't a problem OR another food or foods is still a problem and also needs to be removed before improvement can happen.
We saw no improvement pulling dairy the first time. He was reacting to other things we had to pull as well before we saw improvement. Then I trialed diary, it failed after a week of eating dairy, and it only took a couple days to see most of the improvements after we took it out again.