It's going to be different with every rabbit. Some become rather agressive and territorial at some point early on, while it happens later with others. There's no rhyme or reason to trying to separate them in such a way. Most breeders I know will start separating bucks from does when they're weaning them from their mom, then put the keepers into cages by themselves after a couple of weeks away from their mom while putting the rest into cull cages or meat pens when they're old enough to begin displaying the traits relating to type or color. I started doing so when I raised my first litter, and so far it has worked rather well.