Women in Spain will be offered 3 days of menstrual leave every month: https://www.dailymail.co.uk/news/article-10806329/Women-offered-three-days-menstrual-leave-month-Spain.html

This would total 36 days, that is about 7 work weeks and 1 day, per year (or 36/251 ≈ 14.34%). I could not find any information on whether or not these 3 days are planned to be paid, but it appears not as the first 3 days of sick leave are also unpaid in Spain. However, other countries that have menstrual leave for women pay them for it, and 3 or 4 days per month paid period leave have been proposed in both Italy and India, which sets a worrying precedent:

Why is this relevant for men?

Because paid menstrual leave causes a defacto pay gap, where men get paid less for the same work as they are not afforded the same amount of paid days off.

If it is unpaid on the other hand, it increases the (false) pay gap that feminists have been lamenting, and also gives women massively more flexibility, even if they do not suffer from debilitating period pain, that men don't have. Having a well-paying job and being able to trade some money for a long weekend is a huge advantage, whereas a man who can't or doesn't want to work that much is forced to choose a lower-paying job with fewer or more flexible hours.