Thank you for taking time and answering the questions. However one fact remains unclear , if someone takes on the Din of taking the extra seven days of waiting, there is a chance that she might go over the ovulation periods therfore reducing defacto the chances of getting pregnant, which then is going over a Mitzvah Mideorita for a Din that was accepted by Bnot Yisrael. We all understand the ramifications of the 7 days wating period (how well it keeps the passion going etc...) however knowing that sometimes situations might be more difficult and each case being a case on its own. What are the opininos of some Rishonim like the Rambam, Rashi etc...

Shalom Uverachah, I apologise that it has taken me some time to reply to you. In most cases we have the possibility of solving the fertility issue today thus it is not as acute a problem as you suggest, Baruch Hashem. All Rishonim agree with this and it is recorded in the Halachah in the Rambam, Shulchan Aruch etc. Kol Tuv