Hi - I'm probably the last person who should eb responding to your query as, after 18 months of treatment, I only heard that this test existed recently from my new GP!! Still can;t quite believe my treating clinic never mentioned it!!
Anyway, my lovely new GP sent me to the local hosp and I had to wait about 10 working days.... they may have come back a bit sooner but I didn't get an appt til then - I think

that anything over 30 indicates ovulation has occurred. But you could do a search on here of 'day 21 progesterone' and see what else comes up. (Mine was 41.5 and said underneath it indicated it had occurred.)
Hope that helps, you could give the blood test clinic a ring to ask what their test results times are??
Best Wishes,
Anne x