Does an expiatory offering for an oath (kaffarat yamin) become obligatory for someone who swore to make up missed prayers, but then delayed making up some of them until the following day? And is repentance sufficient instead of the expiatory offering in this case, especially given the difficulty of feeding the poor or fasting?

Whoever missed a prayer or forgot it must hasten to make it up immediately. And whoever broke an oath must offer expiation, which is feeding ten poor people, or clothing them, or freeing a slave. If he is unable to do so, then he must fast for three consecutive days. Mere repentance is not sufficient for expiation; rather, one must perform what Allah Almighty has enjoined as expiation. And shyness from people is not an excuse for abandoning what Allah has made obligatory. You must expiate your oath, and do not frequently swear oaths.