Any time a naked penis is near a naked vagina, there is a chance of pregnancy. Before your period, during your period, a day after your period, a week after your period, a week before your period, a day before your period.
We women don't know exactly when we ovulate, unless we are under a doctor's care and being tested for fertility related things. All it takes is ONE sperm, of the millions produced, to reach the egg that you don't know has been released. There are recorded cases of women getting pregnant at times they didn't think they could get pregnant.