Rabbit growth varies greatly with breed but for typical meat breeds like the Californian and New Zealand the growth chart below does apply. This chart is a collective summary of a study completed by Penn State University of 1000 market rabbits growth. Multiple breeds were involved in the study and the data is an average of all breeds that we have declared "Typical". Interesting enough it does follow the commercial grower schedule of 5 pound in 10 weeks, 5.5 pound in 11 weeks and 6 pounds in 12 weeks.
Yes, there are bloodlines within the Californian and New Zealand bred that are more aggressive faster growers which can greatly exceed expectations in cooler growing conditions with 5 pound fryers achieved in 8-9 weeks. In general 4H rabbits are raised in the hotter months which can greatly reduce growth if corrections are not made in the growing environment to help curb temperatures. An experienced commercial grower operation uses shading and good air flow to reduce temperatures with some actually growing in temperature controlled facilities.
4H and FFA growers need to locate summer animals in full shade with cage shielded such that rabbit and feed cannot get wet. Hopefully this location provides a good cross breeze as well. Cold water at least twice a day is a good thing to the rabbits as well as frozen water bottles in the cage which they can use to self regulate body temperatures. If you want to gage how comfortable your rabbit is put on your Winter coat and stand by their cage.