Alā is a particle drawing attention to an important recollection. Rubba governs a genitive noun and can serve different rhetorical purposes; in this context it conveys multiplicity—many pleasant days.
In rubba yawmin, yawmin is an indefinite genitive noun and ṣāliḥin qualifies it. Minhunna points to the women already mentioned in the account.
Translating rubba mechanically as “perhaps” would misrepresent the line. “How many a day” or “many a day” conveys its context here.