It really varies. I don't know the maximum, but I'll use some of my cats as an example.
We took two female cats for a spaying, one was healthy and normal, the other has brittle bones and no tests have diagnosed what the cause is (all blood work,thyroid, etc., everything normal).
The two cats were spayed within a few minutes of each other. When we went to pick them up, the vet went to see if they were awake. Both according to him were given the same amount of anesthesia. The one with brittle bones was up and playing, chasing her tail. The normal healthy cat was groggy and sickly acting. She remained that way for well on into the next day.
It couldn't hurt to call the vet and just ask, it could possibly be a reaction or something. For some reason it just tends to affect animals differently.