Just to clarify:
Christ’s “once-for-all” sacrifice is eternal. Maybe a wording which cause less confusion than “eternal” these days is “not temporal,” since “eternal” has come to mean “continuing forever,” which is different than the Church has used it in contexts such as these.
That said, it’s interesting if Calvin discarded the correct “eternal sacrifice” of the Mass, while preserving an incorrect notion of eternal sacrifice in Hell.
The word eternal in the Christian context means more than just starting here and going on forever forward. Infinite is a better term and mathematically more accurate; accounting for both time and volume.