WGN Chicago news was showing a segment about thousands of cars lining up for free Covid tests while you sit in your car. Results in 24 hrs, I guess.

So, let me ask......let's say you do not have Covid 19 at the moment of the nasal swabbing and the test results prove it, but on the way home you are exposed and unknowingly contract it. How long does it take for that to show up in another nasal test?

Or, asking in another way, do you really need a test every day to prove no Covid infection?

Or....how long after exposure does it take to show up in a nasal test?

How valid is the test? I've heard less than 50% valid. Correct or rumor?