Is it permissible to invest the ten percent vowed for charity and grow it, then give it out along with its profit and an additional profit, or must it be given out immediately upon availability, in fulfillment of the vow or covenant with Allah?

A vow of obedience must be fulfilled immediately; it is not permissible to delay it, for the Prophet, peace and blessings be upon him, said: (Whoever vows to obey Allah, let him obey Him). The command here implies immediacy. Therefore, it is not permissible to invest the money of a vow because it leads to delaying its fulfillment. This applies to both absolute vows and conditional vows whose due time has arrived.