Is it permissible to pray and fast during the second menstrual period that occurs at the time of ovulation and lasts for two days?

If the second menstruation occurs before 15 days have passed since the cessation of the first menses, then it is istihadah (vaginal bleeding outside of menstruation) which necessitates prayer and fasting, and sexual intercourse with the husband is permissible therein. However, if it occurs after 15 days have passed, then it is menstruation which prevents prayer and fasting, rendering them invalid.