ovulation then pos opk?

[itsnowmyturn]

I have been charting and using 2 apps, they both have me ovulating on cd17, I got a near pos opk with fmu on cd17 but they faded later in the day maybe due to diluted urine, i got a pos opk cd18 with second urine and a near pos with second on cd19.

Is it possible to even ovulate before i get a pos? Or is it more likely that I missed the surge on cd18? I'm confused as to how ff and thbe other app came to the conclusion that I I ovulated on cd17 not complaining tho as we bd cd15