When the test line is equal to or darker than the control line, that counts as your positive. Most women ovulate 24-48 hours after that. There are exceptions to that, of course...some may ovulate earlier or later.
If using 1 vial, most women tend to go for 24 hours past positive. If using 2 vials, many tend to go with 12 and 24 hours past positive.
When we tried 6 years ago, we went with 2 vials and did 12ish and 24ish hours past positive. We conceived on the first try, but had an early loss. Our son was conceived on the next try, using the same timing.
This time, with the price increases, we planned to use only 1 vial per cycle and inseminate at 24 hours past positive. We ended up using a known donor who shipped to us, but that was the plan before we decided to do that.
Mom to P (12), J (11), E (6), and awaiting the arrival of our last baby in late December 2017.