OK, but let's not "scrupulize" people here by finding one of the strictest opinions regarding the matter.
Bishop Sanborn delivered an excellent summary of the matter. On details like the exact length of time, e.g. 74 minutes, where 75 would suddenly constitute mortal sin, those really do vary with the theologian, and, even according to St. Alphonsus, one is not obliged to go with the strictest opinion. When we get weird about details, we have to be careful not to slide over into Pharisaical legalism. Church has always been reasonable, and about common sense. I personally would be a bit stricter on some of these points than what Bishop Sanborn here cites, but not because I believe it binds anyone else's conscience, or even mine, for that matter, but just because I might want to do more than the minimum to the extent that I can do so.