First, there is no way to know for sure when
happened without charting temps and watching for the increase that shows ovulation. Implantation could happen anywhere from day 6-14, usually between 7-10 DPO. There is no way to know how long your implantation was.
As for taking the OPK, cycles vary. Sometimes I O on day 12 or as late as day 16 and I have pretty regular periods. Just keep taking it and once you get a + result you will O from 12-36 hours later.