Is there a ‘good’ time to take a test?

I’m 16, and my period is about 2/3 days late. I’ve been really moody (my boyfriend’s been telling me how crazy my irritability is and I’ve been crying out of nowhere) and tired and overall feeling pretty sick. I’m not sure when it would come out positive, though, since google isn’t the best source when it comes to tricky stuff. He said he’d buy me a test (since I don’t have any money rn), but I wouldn’t be able to take it until about Saturday (since we don’t have school Friday and that’s when I see him). Do you think it would show up then?