The majority of my sexual experience has involved at least a couple of dates beforehand. I don't know if it is a hormonal thing, I assume it is, but to my my mind the number of times the date that lead to sex coincided with the girl either starting her period or being so close she had started by the time we woke up, etc has been such a high percentage of the time I find it impossible to believe it was sheerly coincidental.
So yeah, as far as the whole sex thing and menstrual thing and mixing it all up, not only do I not have any problem with it, I totally approve.