Did I ovulate?

I’m very new to bbt testing, but have been tracking LH for years. My opk was starting to get dark yesterday (the 12th), about a .71. We had sex yesterday morning. Today (around 10:30am) my opk was a definite positive. But my bbt dipped low this morning as well. Could this mean I ovulated extra early, like possibly yesterday? Can you ovulate before you get that sure positive? I’m just really not sure how to read these charts. How do you know when you ovulated according to bbt? Thanks!!