I only have one cat, and I change out the entire litter box every 7-10 days, usually once a week. On top of that, I remove any solid waste daily, as soon as I can to keep the litter box clean. It's a covered box, and from what I read about the urine smelling like ammonia being the cause of some cats refusing to use their litter box, I decided to definitely play it safe. My cat has always been reliable using the box. They said that the cat's nasal area will become uncomfortable from breathing it in...so I didn't want that to happen at all.
It was horrible seeing some of the hoarders on TV. One woman was actually on oxygen in her house, and her daughter and family refused to go over there because of the odor. The cats will have to be fixed for sure, then complete cleaning in order to move forward. Mixing bleach and ammonia can be fatal, glad you won't be making that mistake. Here's some info from another post I wrote:
"We can judge the heart of a man by his treatment of animals." ~Immanual Kant~