My contract also says 72 hours for health/infectious type issues and recommends a visit to a vet within that period of time, but I have extended it for up to a week for certain situations. My contract covers genetic issues (HCM, etc.) for a year, but as Brigitte mentions, claims must be substantiated by tests and/or necropsy.
It's also important to know what that means - for instance, if you have a cat that is diagnosed with HCM the breeder will most likely offer a replacement with the caveat that you return the original kitten, unless it has died of course. Cash refunds do not occur too often, but these things should be specified in a contract and if they're not you need to ask about them.
In my experience, most people don't pay too much attention to the terms of the contract - I guess they just can't imagine anything bad happening to a kitten, even though I ask them to read it through and ask questions before signing... Fortunately I've not had to deal with this sort of problem, and with any luck none of my kitten owners will ever find themselves in such a situation where they have to pull out their contract and read it through again...