Progesterone test before I ovulate?!?

I am just starting on the path to diagnosing our infertility issues. My doctor ordered a blood test on day 21 for progesterone, prolactin, AMH, TSH, and FSH. I asked him if it was fine to test progesterone before I ovulated, because that seems stupid, and he said it would be fine. I came home and read more about it, and it doesn’t seem like it’ll be useful. I’m having fluctuating cycle lengths but the last one was 36 days and I ovulated on day 22 or 23. I know he’s a doctor but I’m a lawyer and I still sometimes overlook something obvious with my clients, especially when I am rushing. Is there any reason to believe the test could be useful on day 21 even if I haven’t ovulated by the time I take the test?