The testFRWD test cycle for maximum event security
A negative PCR test result means that at the time the sample is taken, the person tests negative. But the same person can become infected after the test, in the worst case just minutes later. Which means that it is important to know how long it takes for this person to become infectious.
ACP Journal (model to all global cases): average incubation period—the time between exposure to the virus (becoming infected) and symptom onset:
This is the reasoning behind the 4-day PCR test travel rule implemented by most governments world-wide.