"But this also has a bearing on our firmly holding the conviction that there were really six days on which the Lord created everything, in contrast to the opinion of Augustine and Hilary, who believed that everything was created in a single moment. They, therefore, abandon the historical account, pursuing allegories and fabricating I don’t know what speculations. However, I am not saying this to vilify the holy fathers, whose works should be held in high regard, but to establish the truth and to comfort us. They were great men, but nevertheless they were human beings who erred and who were subject to error. So we do not exalt them as do the monks, who worship all their opinions as if they were infallible. To me the great comfort seems to lie rather in this, that they are found to have erred and occasionally to have sinned. For this is my thought: If God forgave them their errors and sins, why should I despair of His pardon? The opposite brings on despair—if you should believe that they did not have the same shortcomings that you have. Moreover, it is certain that between the call of the apostles and that of the fathers there is a great difference. Why, then, should we regard the writings of the fathers as equal to those of the apostles?" [Luther, M. (1999, c1958). Vol. 1: Luther's works, vol. 1 : Lectures on Genesis: Chapters 1-5 (J. J. Pelikan, H. C. Oswald and H. T. Lehmann, Ed.). Luther's Works (1:121). Saint Louis: Concordia Publishing House].
"Hilary and Augustine, almost the two greatest lights of the church, hold that the world was created instantaneously and all at the same time, not successively in the course of six days [Hilary, On the Trinity, XII, ch. 40, Patrologia, Series Latina, X, 458, 459; Augustine, De Genesi ad litteram libri XII, IV, ch. 33; Corpus Scriptorum Ecclesiasticorum Latinorum, XXVIII, Sec. III, Part I, p. 133]. Moreover, Augustine resorts to extraordinary trifling in his treatment of the six days, which he makes out to be mystical days of knowledge among the angels, not natural ones. Hence debates are customary in schools and churches concerning evening and morning knowledge, subjects brought up by Augustine and scrupulously propounded by Lyra. Whoever wants to gain a knowledge of them, let him get it from Lyra" [Luther, M. (1999, c1958). Vol. 1: Luther's works, vol. 1 : Lectures on Genesis: Chapters 1-5 (J. J. Pelikan, H. C. Oswald and H. T. Lehmann, Ed.). Luther's Works (1:4). Saint Louis: Concordia Publishing House].
Addendum: Catholic Answers
"The writings of the Fathers, who were much closer than we are in time and culture to the original audience of Genesis, show that this was not the case [a consensus on literal days of creation]. There was wide variation of opinion on how long creation took. Some said only a few days; others argued for a much longer, indefinite period...Catholics are at liberty to believe that creation took a few days or a much longer period, according to how they see the evidence, and subject to any future judgment of the Church (Pius XII’s 1950 encyclical Humani Generis 36–37). They need not be hostile to modern cosmology." [source]