This is about as specific as the council bishops get:
As regards the readings, the following shall be observed:
a) Readings from sacred scripture shall be arranged so that the riches of God’s word may be easily accessible in more abundant measure.
The Vatican II theme: accessibility and abundance.
b) Readings excerpted from the works of the fathers, doctors, and ecclesiastical writers shall be better selected.
Non-Scripture readings are valued in the tradition of the Hours.
c) The accounts of martyrdom or the lives of the saints are to accord with the facts of history.
Modern rationalism, eh? With the ancient saints, history doesn’t even enter into the picture because the early accounts were not literal in the same way modern news accounts and written history would be. Personally, I would have no problem with the more apocryphal accounts, assuming that the really excessive aspects were minimized and the spiritual value was clear.