When to start TWW count-down?

Just wanted to confirm does the tww starts the day after you take the trigger shot, or the day that you actually ovulate. The nurse told me today that once I take ovidrell shot I don't have to OPK any more. Last month I did and got a positive a day after the shot. I was also told that if I don't get AF 16 days after last BDing only then to come to the clinic But that would mean that tww is actually longer.
Answers:

I think you start the day after. I always count day after as 1DPO


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