Answer: The incubation period of the stomach flu is usually about 48 hours but it can vary.
It generally takes about 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. I have heard that the new strain of Norovirus GII.4 Sydney can strike in less than 24 hours but usually 24 hours is the minimum. 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 in her face.
My sister has 5 children. They caught the stomach flu from relative 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 the stomach flu. My neighbor did not get sick until 9 days later. Another friend told me taht 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.