Should he allocate time to a wife who is menstruating or in nifaas?
Question

                Should a man who has more than one wife to consider his menstruating wife or who has post-natal bleeding when he divides his time among his wives?.
Praise be to Allah.
    The basic principle is that it is obligatory to divide his 
    time between both, based on the principle of justice between co-wives. 

    But the custom in many countries is that when a woman gives 
    birth, she stays with her mother for forty days or less, so that her mother 
    can look after her, or her mother may come and look after her in her own 
    house. In either case, he is not obliged to allocate some time to her, and 
    she may agree to waive her right to a share of his time. 

    Shaykh ‘Abd al-Rahmaan ibn Naasir al-Sa’di (may Allaah have 
    mercy on him) was asked: Is it obligatory to allocate a share of time to a 
    wife who is menstruating or in nifaas? 

    He replied: 

    The well known view in our madhhab (the madhhab of Imam 
    Ahmad) is that he must allocate a share of time to each of them, because 
    they are both wives. But the correct view which should be applied is that 
    the menstruating wife has a right to a share of his time, but in the case of 
    one who is in nifaas, she does not have a right to a share of his time 
    according to custom and because the woman in this situation usually agrees 
    to give up that right; in fact in most cases whilst a woman is still in 
    nifaas she does not want a share of her husband’s time and this is a view in 
    our madhhab. End quote. 

    Fataawa al-Mar’ah al-Muslimah 
    (2/693). 

    And Allaah knows best.