We recommend putting the jelly in the fridge for a minimum of 4 hours, There are a couple of reasons that the Jelly could take longer than 4 hours to set. Firstly, check that the fridge is set to the recommended temperature - 3 degrees. If it’s too warm the jelly won’t set. Secondly, when you mix up the jelly - make sure that you are adding the correct ratio of powder to water. If there is too much water compared to powder then the jelly will not set.