Without reading the entire thread, it depends on the comfort of the woman and the man with it.
If it is established that it is a no by either party, then that's it.
If both are in agreement, first, learn the amount of days the cycle last and the flow pattern. If the low flow is at the beginning or the end, get it in.
If you just can't wait, and her vagina is burning with desire, take a bath or a shower, lay down a towel, and get after it.
We have to change the culture on this. A woman's cycle is LIFE!
My great grandmothers put their cycle in the garden and had wonderful gardens...shit is better than epsom salt.
We ALL come from, the very thing we deem nasty, just fertelized.
It's to each his own, but respect the placenta.