Is it permissible to delay the fulfillment of a financial vow (nathr) and pay it in two or three installments due to difficult financial circumstances?

If you vowed to donate a sum of money every month, you must fulfill the vow before its specified time expires. If it expires, you must offer an expiation for breaking an oath (kaffarat yameen) in addition to fulfilling the vow. However, if you did not specify a time, you may collect the amount and donate it for the past months, as fulfilling the vow in this case can be done at leisure.