The old urine I do wash off after an hour or two because of the smell, but I let it dry on my skin and let it penetrate with a massage.
If you let it age in a jar they say that it should breathe because the oxygen is needed to transform the urea in ammonia. I did some small holes in the lid with a nail and the other time I used a mason jar (I identified it ammonia - for the curious) and put a paper towel instead of the metal lid...