When to test with digital

Ok so as of tomorrow ill be 4 days until af...i have 1 digital clear blue with weeks estimator left. ..ive heard digitals wont show a bfp unless u r past when af is due...has anyone taken 1.. 4 days before af and had any luck..i swear im nauseous and keep getting dizzy and hungry and lots of preg symptoms but not sure and i hate waiting lol lemme know what ya think!!!!!