What is the Sharia ruling regarding a wife's deferred dower (sadaq) for one of two terms? And is the husband obligated to give the wife the deferred dower upon request?

It is permissible to defer the sadaq (dowry)—whether in whole or in part—to a known date. However, it is not permissible to defer it to an unknown date, such as death, divorce, or harvest time, according to the majority of scholars. The Hanafis, however, permit deferring it to an unknown date. As for the Hanbalis, they permit deferment without specifying a time if no term is mentioned, and it becomes due upon separation, but it is not valid according to them if the term is unknown and specified by a time. The most preponderant opinion is that it is permissible to defer the dowry only to a known date; otherwise, the woman is entitled to the dowry of her peers (mahr al-mithl). If a dowry is specified but no deferment is mentioned for it, then it is immediate, and the woman has the right to demand it forthwith. If the known term arrives, the woman has the right to demand it, and the husband must pay it unless he is in financial difficulty. However, if the term has not arrived, she does not have the right to demand it except upon separation by death or divorce.