Iv never done OPKs before so my SO And I went out last night and bought a box of the first response and yesterday was CD16 I took the first test around 9pm which is the top test and then I just retested at about 10:30am this morning CD17. The app is estimating my ovulation for tomorrow. Today’s test is much darker but is it positive yet? We have never done this before and I read that women get a dark but not dark enough line and then it goes away. Would the change in these test indicate a positive is coming?