I had to eliminate dairy with my son (and he most definitely DOES have an allergy, he broke out in hives when consuming it himself until just recently at 18 months) and the difference was almost immediate, like within a couple of days. I wasn't eating tons of dairy and although it takes a couple of weeks to clear completely most babies do have a marked improvement within a few days. Some take longer if they have a severe allergy and are very sensitive. Even with my son who broke out in hives from consuming it himself, I did not have to cut out hidden dairy. It just depends on the child and how severe their symptoms are. It could also be reflux not related to an allergy though since her poop is normal...