pax vobis - I think st. paul when he said "for a time" was referring to spouses practicing continence, which means avoiding sex entirely. And, that it was not for spouses to "for a time" have sex with the intent of avoiding children with 99% accuracy. If that is the case, then "for a time" unmarried catholics can "comfort" themselves and mirror the "comforting" occurring in catholic marriages. If it is true that "for a time" we can do this as pius xii says, then "for a time" unmarried catholics can fornicate. It is that simple. But, that is not the case. So, we can not "for a time" practice pius xii rythm.
Lastly, I have a point to make about how it must have the approval of ones priest. This is faulty in the sense that a priest does not have the fullness of the sacrament of orders. It would have to be approval of a bishop, which obviously means for each case. But, it is not. Because, a bishop, a successor of the apostles, would never allow for such foolish measures and in turn, sin. It is for one, impractical to an extreme, and the faith is practical. And, two, simple ones like myself would learn about these proceedings and would have to publicly reject it and correct the bishop, which would be successful. The pope has always tried underhand measures against the bishops, and this is in harmony with it. "Keep it quite, keep it in the confessional". The serpent is the most cunning of all creatures. The bishops of the catholic church have been marginalized so much over the centuries, that it is only when they all become heretics that the pope grants them their God given rights.