Hi Colourprinter and Jaetee.
I had two natural cycles after stopping the pill, ranging from 30 to 35 days. On the safe side, I used OPKs starting from around day 11 until I got a positive LH surge on day 19. I started on day 11 because one of the biggest textbook myths is that you ovulate on day 14 (if only we all did!). As it turned out I ovulated on day 19 so it can happen later for some folks.
Jaetee, I know it's frustrating to constantly "pee" on that stick and see no positive result, but perhaps testing for longer might help. I felt like I had to wear different disguises each time I went to Watsons to replenish my OPKs, but just to satisfy my own curiosity I kept using them. I also charted at the same time so I was lucky enough to see a corresponding increase in my basal body temperature.
I'm not sure how fast the turnaround time is for blood tests which test ovulation in HK. I know in Australia if you take a test in the morning they can sometimes have the result by the afternoon. If it's not immediate, but you get a positive result, at least this might de-mystify when you ovulate. Hope this helps!
Best wishes. Autumn.