In my experience anal is either happening or it isn't. Time of the month is nearly irrelevant. The only factor it might play is that some woman get very easily aroused during that time.

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Put me on wheels and I'll turn tricks.

Clever? Nah, I ran out of that years ago. But if you find this, let me know, k?
"The road goes ever on..." ~ Tolkien

In memory of my friend skip...
Go then, there are other worlds than these