We know that Agostino reaches Rome "on the fourth day after setting out" (Chapter 4.VII) and, on that same day, Galeotto reaches Pagliano and starts immediately for Rome.  Presumably he arrives a few days later and frees Agostino instantly; we know this happens on September 3.  Agostino's statement that he "had not seen [sunlight] for a full week" (Chapter 4.IX) is impossible; Galeotto cannot have taken a week to free him.  We conclude that Agostino meant to say that he was in the hands of the Inquisition for a week, and therefore was taken August 27.