About 10 hours the time I had true food poisoning. Ate bad chicken at probably 6:00 p.m; was feeling icky by about 10:00 p.m. Woke up at 4 a.m. and vomited and then did it again at about 11 a.m.

Other times I've eaten food that has upset my stomach, it's happened from anywhere within 10 minutes to a few hours - but in those cases I didn't vomit.