Wiktionary
time of the month
alt. (context idiomatic euphemistic English) The time when a woman is menstruate or about to. n. (context idiomatic euphemistic English) The time when a woman is menstruate or about to.
Usage examples of "time of the month".
If not for the soaked rags she'd carefully buried to one side of their path or the other, she wouldn't have had a clue that it was her time of the month.
But sex could not be involved-except at a certain time of the month.