Differing Days

Quintam Tychonius regulam ponit quam De temporibus appellat, qua regula plerumque inveniri vel conici possit latens in Scripturis sanctis quantitas temporum. Duobus autem modis vigere dicit hanc regulam, aut tropo synecdoche aut legitimis numeris. Tropus synecdoche aut a parte totum aut a toto partem facit intellegi, sicut unus Evangelista post dies octo factum dicit, quod alius post dies sex, quando in monte discipulis tantum tribus praesentibus facies Domini fulsit ut sol et vestimenta eius ut nix. Utrumque enim verum esse non posset, quod de numero dierum dictum est, nisi ille qui dixit post dies octo, intellegatur partem novissimam diei ex quo id Christus praedixit futurum, et partem primam diei quo id ostendit impletum, pro totis diebus duobus atque integris posuisse; is vero qui dixit: post dies sex, integros omnes et totos, sed solos medios computasse.  Sanctus Augustinus Hipponensi, De Doctrina Christiana, Liber III

The fifth rule Tychonius gives he names 'of times', by which one can frequently discover or conjecture quantities of time which are not declared in Scripture. And he says that this rule is applicable in two ways: either to the trope of synecdoche, or to legitimate numbers. The trope of synecdoche would have the part for the whole, or the whole for the part understood; as when one Evangelist says it was after eight days, 1 and another that it was after six days 2 that on the mount in the presence of the three disciples the face of the Lord shone like the sun and His garments were as white as snow. Now both of these statements cannot be true, unless we suppose that he who says 'after eight days,' should be understood as counting the latter part of the day on which Christ spoke of the future, and the first part of the day on which he showed its fulfillment as two whole days, while the writer who says 'after six days', reckoned only the whole unbroken days between. Saint Augustine of Hippo, On Christian Teaching, Book 3 1 Lk 9:28 2 Mt 17.1