You should separate them now, because a rabbit can become pregnant again just before or immediately after she’s given birth to a litter, and if that happens, she won’t be able to nurse the first litter properly. You can get a bunny girl spayed before she’s had any babies, it’s not necessary for her healththat she has one litter before she is spayed. Once the doe and the buck have been de-sexed and have healed (healing takes about a month), they can live together again. Male rabbits can have live sperm for one month after their neuter.
If you suspect the does is pregnant, you should give her extra food, f ex pellets for young rabbits.
9 months is very old for rabbits to start mating, a girl rabbit can get pregnant at 5 months, boys become sexually mature even sooner. Are you sure they are of opposite sexes? It’s fairly easy to see if a boy is a boy, because they have testicles, but it’s a lot less easy to see if a girl is a girl.
The Binky Bunny Forums doesn’t allow discussions about intentional breeding. There is another rabbit-forum, Rabbits Online, that has a special section for discussions about breeding. It’s called the “Rabbitry and Show-Room”. http://www.rabbitsonline.net/