Time to set up really depends on a number of factors, including the type of stove you're using to cook the jelly. It will likely take a good 30 to 45 minutes, maybe longer for your jelly to set. And even as you remove it from the stove, it won't be completely set; in fact, it will be more like liquid. As it sits in the jars and begins to cool, the jelly will firm up and set even more. That's why it's important to put it in jars right away.