Is a vow to fast for one week sufficient to fulfill the request for marriage, or should the fasting period be extended to one month?

Conditional vows are disliked (makrooh), but they must be fulfilled if the condition is met, based on Allah's saying: "And let them fulfill their vows," and the Prophet's (peace be upon him) saying: "Whoever vows to obey Allah, let him obey Him."

Therefore, you must fulfill your vow and fast for a week if you get married.

Know that a vow neither brings something forward nor delays it. Only what Allah has decreed and predestined will occur, as the Prophet (peace be upon him) said: "A vow does not bring anything forward nor delay it; rather, it is used to extract (money) from the miser," and his saying: "Do not make vows, for a vow does not avail anything against destiny."

Therefore, we do not advise you to add anything to your previous vow.