In simplistic terms, with the old fashioned (and more enjoyable) method of procreation, the man could withdraw at any time up until the implantation of his seed in the woman.
Surely this is what these two men have insisted on doing, although modern scence has allowed fertilization to preceed implantation in these cases.
Maybe sperm and ova should be seperately frozen, and combined immediately before implantation if (and only if) both parties still wish to continue.
However, I seem to remember another case in the last couple of years where the widow of a British serviceman was allowed to use his frozen sperm for conception. (presumably he left her everything in his will?)

Nigel