Where does Augustine say that Adam and Eve were in Eden for just six hours before sinning? In Calvin's Commentary on Genesis, he spends some time dealing with the question of how long Adam and Eve were in the garden of Eden together before they sinned.  He writes:


  The opinion has been pretty generally received, that they fell on the day they were created; and, therefore Augustine writes, that they stood only for six hours. (commentary on Genesis 3:6)


I haven't been able to confirm that Augustine actually wrote this.  I have found mention of six hours in Dante's Paradiso (Canto 26), but so far nothing from Augustine.

Did Augustine say six hours, and if so, where?
Did Augustine say six hours, and if so, where?


Probably not.


  Finally, Calvin erroneously claims Augustine for the view that Adam
  and Eve fell after a mere six hours. (emphasis added)


This is from John Calvin: Student of the Church Fathers1 in which Lane references Saint Augustin dans l’oeuvre de Jean Calvin2


1. John Calvin: Student of the Church Fathers (Anthony N. S. Lane, A&amp;C Black, Jan 1, 1999, p.220)
2. Saint Augustin dans l’oeuvre de Jean Calvin (Luchesius Smits,
 Van Gorcum, 1957)