I thought to add that instruction as it's not on the website and it's ridiculously difficult to read it on the bottle label (which happens to be in German and French only!)
I used it on a urine stain on a carpet that was cleaned 2 months ago but still had a slight smell. I sprayed it generously and cover it with cling film overnight. It really did the trick: the smell is completely gone and the treatment has not damaged the carpet (which is bright green). Great product, in my experience.
I really needed to find a good cleaning product after my new cat peed on the sofa. Thanks to zooplus, I found UrineOff. First I applied about a quarter of the bottle, and then the next day around the same amount. You could still smell something for a couple of days, but now the smell is totally gone. This is a really good product!