I tend to have shorter cycles and so ovulate early. I started charting with FF and OPK's recently, and last cycle I got my first +OPK on CD8. I then had + on the next day, with an on-the-fence almost + on the morning of CD10. FF first pegged my O day as CD8, then ended up moving it to CD10.
This cycle I got my first +OPK two days ago on CD10, had another + last night, and clear negative this morning, CD12. From what I've read, typically you O on the last day of +OPK, not the first, so if you've had a +OPK today keep testing over the next few days to see if you are having a longer surge.
At any rate, welcome and best of luck!