It depends on your cycle and when you have time, but I just started to use them this month (first real month TTC #2). I started testing in the morning from CD10. I usually ov around CD16, though last month it was 17. Ideally, the best time to do them is afternoon or early evening, but I work and often don't get home til early evening some days, so testing regularly is a bit of a hassle unless I do it in the morning. So I did it every morning from CD10. They were clearly negative until CD13 when I got a nearly positive one in the morning. So then I tested in the evening on CD13 just to confirm that it would be positive (it was). I tested again morning and evening on CD14 just to confirm the LH surge had happened and was done. Basically, you get a surge of hormones about a day or two before you ovulate and that's what you're testing for. So I kept testing until the positive began a definite negative again, which was the evening of CD14, and I'm pretty sure I ovulated on CD14, about 12-24 hours after that positive reading.