The amount of radon present in your home doesn’t remain constant over time. It’s actually considered normal and typical for it to rise, fall, and fluctuate over the weeks and months of the year.
Some houses are much more likely to experience drastic fluctuations than others. Radon tests that continue over long periods of time are considered much more accurate for that reason. Long term tests are many times more likely to pick up on the full range of radon levels that are normal for a given home. For best results, try testing for a minimum period of six months. A year would be even better and safer, so definitely consider going that route if at all possible.