If I'm going for constant litters, I rebreed at four weeks
That way the babies will be about 8 weeks by the time the new ones are born and can be on their own
I like to rebreed my lops at four weeks. I wean the original litter at around 7 weeks, and the doe gets a week of rest between each litter. So, pretty much the same as RabbitsOfTheCreek.
While I don't have a ton of experience yet I've been breeding all of my rabbits back at about 4 weeks as long as the doe is in good condition. I'm thinking about bumping it to 6 weeks. I just got Hollands recently and still have a few weeks until my first holland litter