I wouldn't be surprised if the speed of onset of food poisoning symptoms was related to the degree of contamination. A greater degree of initial contamination would probably lead to greater bacterial replication in the gut and speed things up.
Just how bad can contamination get? In my youth, I worked a couple of summers as an usher at a movie theater that was part of a large chain. The refreshment counter sold hot dogs that rolled all day on hot metal tubes.
After the close of business one day, I was in the back room and I saw another employee putting that day's unsold hot dogs back into the refrigerator. I had kind of assumed that they threw out what went unsold each day, but, apparently, I was wrong. I then noticed that the other employee was also picking out a few of the unsold hot dogs and disposing of them.
"How do you know when it's time to throw them away?" I asked. "When they start to turn green," she said. I laughed at first, thinking she was joking, but she wasn't. She showed me one of the "expired" hot dogs. Despite rolling on hot metal tubes for who knows how many days, it had several green patches starting to form on it.
I haven't had a theater hot dog since.