You will often get 2 lines without ovulating, but unless the second line is as dark as or darker than the control line, it is still counted as a negative.

Some women never get a true positive, but take their darkest negative as a positive if it's the right time. It can be hard to catch your surge if it happens at the wrong time of day.

You shouldn't get true positives at times you are not ovulating. If you are seeing 2 dark lines at the right time, I think you can be reasonably sure ovulation will happen within the next 12-48 hours. Though having said that, the only way to tell for sure if you are ovulating is by temping, or having blood tests.