BTW - sleeping with two women (assuming you get lucky Friday with Mary) is not a good idea. Yes they "know" of each other right now, not really sure where the other stands in your life, but jealousy will rear its ugly head in time and you are going to be the one lashed to pieces by one or both of these women.
If things progress with Mary in that you want to regularly date her and she is your girlfriend, then you have to tell Rhonda you cannot sleep with her any longer. If she hits the roof then she hits the roof. You can't continue having your cake and eating it too because it really will bite you in the ass.
Of course if you don't care about either of them a whit, then carry on as you are.
You stud muffin you!!!!
I know what you mean about the timeframe. Yeah physically you could do two nights but it is the setting of the trap (I mean ... stage) that you want time for in order to seduce Mary. I reckon if it were the other way around - you sleep with Mary Thursday and Rhonda Friday, then you would not have a problem because you would not be making the place nice and prepping for Rhonda.