Is one obligated to fulfill a vow to pray two nights a week reciting the Qur'an, if doing so might affect one's studies?

Vows are not prescribed in Islam, and the Prophet, peace and blessings be upon him, forbade them, saying: "Indeed, it does not avert anything; rather, it is used to extract from the miser." Nevertheless, a vow of obedience to Allah must be fulfilled. The expiation for an oath is: feeding ten poor persons, or clothing them, or emancipating a believing slave, or fasting for three days if one is unable to do the preceding.