What CD to start testing with OPKs?

Emily • Isaac 4/11/18 💛 Rainbow 🌈 Averie 💗 7/5/20
I have a regular 30ish (give or take 2 days) cycle but I have no idea when I ovulate (hence the OPKs). This is my first month using OPKs and i've read some women ovulate earlier on so should I begin testing earlier in my cycle since I have no idea? I just don't want to miss it.. Around what CD should I begin testing?