I’m sorry but the answer is not what you want
There really is no answer to the question of how long do hives last. It is different for many people and depending on the severity of the case, it can be over with in a pinch or it can take quite a while. Myself, I don’t really want to deal with that problem for a single day so I always have the homeopathic treatment oxyhives available at my home. It’s some great stuff that really works but you have to stock up on it because you can only find it on the web. I’m sure this will change soon but in the meantime, you’ll have to wait.