Is it permissible to give the father a portion of Zakat funds for him to keep and spend later on equipping his poor niece for marriage, knowing that the time of marriage is currently unknown?

It is not permissible to deposit zakat with a father to be delivered to a needy girl later, as the ownership of zakat by the poor person is a condition for its validity. Zakat must be promptly delivered to the girl if she is currently eligible, and it is not permissible to delay it beyond its due time. If the girl is not eligible at the time zakat is to be disbursed, then another eligible recipient must be sought, and it is not permissible to wait for her. If the girl needs provisions before zakat is disbursed, then it is permissible to give her zakat at that time according to her need, without extravagance.