OPK when to start

Ok ladies so I bought the clear blue advanced digital ovulation predictor kit last night. I'm confused as to when to start though. The chart says cd9 but glow says my fertile period starts the 8th and ovia says the 10th. I don't want to miss my peak. But I don't know when to start testing because I'm now on day 5 of my period with no end in sight. Usually it's 4 days max and day 4 is super light. Here we are day 5 and it's the same flow it's been the whole time. It slowed down and almost stopped but picked back up.