It really depends on what you want to get out of your rabbit. Health? Production? Quality? Quantity? I know some people on certain homesteading sites will breed back as many as 8 times a year (or about every six weeks). Some of us breed every 12 weeks. How quickly you will need to turn over your does increases exponentially. I've had five year old does still popping out 6-10 kit litters by breeding back every 12 weeks.
The longer a doe goes between litters (within reason) the bigger and healthier the litters you can expect to get will be, the longer the doe will be breedable, and the better condition the doe will stay in. But it seems like the average wait time is 8-10 weeks. I think anything under 6 weeks in inhumae and inefficient as the doe gets no chance to recover from nursing each litter and will quickly loose condition.
Incidentally, unspayed doe rabbits over 6 years old have high tendencies of reproductive cancers and at about 8 years old that figure reaches nearly 100%. But under 4 years it's almost unheard of. Just some food for thought for doe retention time.
Thank you very much. Those are exactly the type of answers I was looking for. A couple more though. At what age do you typically wean the kits? How long do the kits need to nurse? Is there a benefit to weaning at a certain age or is it more beneficial to leave them with the doe for a longer period of time?