Questions before treatment

Start of treatment - first day of menstruation

Dear PAN Team, I am a little confused about the first day of menstruation and thereby the start of stimulation. Currently the first day for me is associated with the usual symptoms (slight pulling or similar), but usually minimal bleeding, albeit red. It's not until the next day that I have a real bleed. In this case, does the first or the second day count for the start of treatment? Thank you very much for your answer. With best regards