theoretically, the 'early testers' should be able to give you a positive as early as 7-10 days after you had sex. However, only with a very low accuracy.
In order to get the 98% accuracy rating working for you, then you need to wait at least 14 days after you've had sex to get a reliable result, or better yet, 21 days i.e.- 1 week after you miss your period.