Is a woman's fast valid if she performs ghusl and intends to fast after 11 days of premature birth and intermittent bleeding? And does nifas have a specific duration before which ghusl is not permissible?

The blood discharged with childbirth is postpartum bleeding (nifas). There is no minimum limit for its duration, but its maximum, according to the preponderant opinion, is forty days. Purity from nifas is achieved by the emission of the "white discharge" (al-qassah al-bayda') or by complete dryness. If the bleeding stops but complete dryness has not occurred, then the nifas is still ongoing. If it exceeds forty days, it is considered irregular bleeding (istihadah), unless it coincides with the time of menstruation. Blood or yellowish mucous discharge is considered part of nifas as long as clear purity has not manifested. Therefore, as long as the bleeding has not completely stopped, the woman is still considered in nifas, and fasting is not permissible for her.