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Actually all gastric bugs take between 3 and 72 hours to first show but the 'show' can be a slightly elevated temperature which isn't normally picked up in adults, they just think they are a bit tired. In kids they puke first, suffer second, but adults are the reverse.
There are always gastric bugs around - you just only suffer from them if you are run down - you've probably all had it but some of you will be immune from past infections and some will have just batted it off!