It's probably easier learning to look for other ways to see whether you're in your fertile phase, leading up to ovulation there can be symptoms such as bloating and pains (as the egg is ripening) and the cm changing to egg white, the cervix rising and opening up. When the opk is positive you should ovulate after 24-48 hours after so it's hard to tell when the ovulation actually happens but on that day and them around it it's when your fertile and should so to speak cover your days by Dtd as sperm lives to up to a week in the womb x