TWW time!!! When to start progesterone pills?

Ma

quick question because I'm doubting the info I have. did clomid and trigger. Trigger was the 16th PM. Nurse said to start progesterone the 19th. but I dont think I should start until the 20th or 21st. (last round trigger was Monday nights she told me to start Weds, clearly no results I think I took too soon!!) what did you do, and did it result in BFP?