Outdoors is dangerous predators (coyotes, dogs, other cats, hawks -yes, they'll take a cat in the blink of an eye, raccoons,,,), cars, bad people, and illnesses. Most die from them before they build up an immunity. Get a primary vet you trust and get their vaccinations. Keep them inside to be safe healthy and there when you need to cuddle them. Worrying about their safety and where they are when they're late coming home, sort of defeats the 'cats relieve stress' part of cat ownership.