Because it is only 90% accurate (that is, the one usually done at vets) and you have no way of knowing whether the queen is actually incubating the disease in question, if it is the test will be negative even though the queen is infectious!

There is not one known case of FIV being passed through sexual contact, it isn't going to happen unless she bites the boy, and they don't wait around long enough to be bitten. Plus she has to catch it herself first - by being bitten by an FIV positive cat.

And for FeLV there is a very effective vaccine, besides which the way that is spread (shared food dishes etc) is easy to avoid totally, just put the girl in with the stud for actual matings.

Obviously if you want to insist on a 24 hour test that is your right, you are in the majority and no-one is going to argue with you. Just don't imagine it gives your cats any more protection than getting them vaccinated against FeLV and using supervised matings, it doesn't!

Liz