False Negative?????

OK, so my Mom works in a Nursing Home down in Florida, 2 of the Residents died from Covid, She got tested Monday the 10th, My Dad was visiting her at the time, He left Tuesday last week giving her a Kiss Goodbye, she became symptomatic on like Wednesday her test came back Positive on Friday, my dad began showing symptoms (like those of a cold) on late Saturday afternoon (having been isolating since Wednesday), His Pulse Oxygenation is in normal range and his temp is fairly close to normal. He got tested Yesterday (Monday the 17th) He got his results back today and they where Negative.

What are the odds of a False Negative with the current tests being used in Georgia?