Answer: The incubation period for stomach viruses is usually about 24-48 hours but it can vary.
"Stomach flu" is just a nickname for viral gastroenteritis. It is not related to influenza, the real flu. It generally takes about 24-48 hours from the time you swallow the virus (norovirus or others) to the time when you start to feel sick1. However, it can easily be less time or more time. It was exactly 51 hours from the time I took my 22-month old son to the indoor playground to when he started vomiting from rotavirus. Norovirus can occasionally strike in only 12 hours. Adenovirus typically has a 1-week incubation period2. However, the incubation period can vary from person to person even when dealing with the same virus. In a recent bout of the stomach flu (viral gastroenteritis) in a friend’s household, the 5 year old got sick exactly 2 days after the 1 year old. However, the mother didn’t come down with it for exactly 1 week after the 5 year old threw up on the mother's face.
My sister has 5 children. They caught the stomach bug from qvrelative they saw on Christmas day (Friday, December 25, 2009). My sister's first child got sick on Sunday night, 2 others on Monday night, and a 4th on Tuesday. However, my sister did not get sick for 8 days after the first child. My neighbor's 2 year old daughter recently got a stomach bug. My neighbor did not get sick until 9 days later. Another friend told me that her 1 year old did not get sick for exactly 2 weeks after their fist child. So incubation periods can vary. I would not consider yourself spared until it has been 2 weeks.
It is very important to clean with a product that actually kills norovirus when a stomach bug is in your home such as the Clorox® Hydrogen Peroxide Spray
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--Annie Pryor, Ph.D.