I realise this is a slightly old post, but I thought this might be helpful info for the future. The ovulation tests pick up a surge of LH hormone, which comes before you ovulate, the range is between 12-48 hours before you ovulate, but for the vast majority of women it is more like 24-36 hours.

So in your example you most likely ovulated cd 16, perhaps even into 17 (24-36 hours after the +ve test). I hope this isn't taken as rude, it just might get you a few extra days peak fertility time.

Your fertile time is generally considered to be from about 5 days before, peaking the day before (as in the day you get you +ve ovulation test) and the day of ovulation (the day after, maybe 2 days after the +ve ovulation test), with it dwindling into the nothing the day after.

So in your example you would have a chance from cycle day 12 ish (11 at a long shot), and right up to cycle day 18 you could still have a very slim chance, but 16 and 17 are the most fertile days. I hope this makes sense and is helpful, and very best of luck.