OPK high means you're in your fertile window, so best to try today or tomorrow lah, that's when you're most likely to conceive! Regarding your late period on day 9 with negative UPT, it's a bit tricky because sometimes stress or hormonal changes can delay ovulation, so the high OPK reading might just be coming later than usual for you. Memang boleh try during late period phase, tapi honestly jika period lambat lebih dari expected, better check with your doctor to make sure semua normal, they can give you better picture of what's happening with your cycle especially if ada changes. Fingers crossed for you!