The two litter thing is still out for debate, there is hearsay and then there is scientific articles against it. The rabbit has two horns, but not two uterus (pl) , it seems that the changes that occur in pregnancy would make it not likely that the doe would ovulate again, or that the womb would be ripe for implantation.
Anyway, after mating, the doe releases eggs 8-10 hrs later, which is why some people bred again after 8-10hrs.
I stopped doing that awhile ago, as I have found that my does produce large litters in one single mating session, where the buck only services her ONCE. Most of my does will not accept the buck after the first mating session, and have litters of 7-10 kits. the amount of eggs released is determined by the doe, and is hereditary, and there are millions of sperm that live 48-72hrs, that's plenty of time for fertilization.