Would The Egg Be Matured Enough For Collection On Day 12 Of Menstruation Cycle?

I am now on day 10 of my cycle and the dominant follicle measured about 17mm and i was given the trigger to take later on with a view to egg collection a day after tomorrow. I asked my fertility specialist if this was not too early and she said no and that she wanted to catch the egg before I ovulated. I normally get an ovulation surge on day 13 or 14 and i have been tracking this for years. My question is would the egg be matured enough for collection on day 12 as planned. My fertility adviser says yes but I am worried and needed a second assurance about this and follicle size. By the way, I am doing a natural cycle IVF with no drugs whatsoever apart from the trigger I received today. By the way, I have no fertility issues but just tryong to have a child with use of donor sperm. Thanks