A friend has been picking my brain about releasing some coturnix quail on his farm. He just wants to see them around and realizes they may not do that well. It's not something I would personally do, but it's his farm and his right to do so. I respect that freedom. I answered him and thought others would like to glean info on Jumbo Brown quail from my response.
Jumbo Brown are considered adults between 6-10 weeks. Some JB breed and lay eggs earlier than others so it can vary bird to bird. I imagine they could be released at 6 weeks or so.
You'd probably have better luck with the Bobwhites if you can find someone raising them. They are not as domesticated and should do better in the wild. I've had them before and they are more jumpy/wilder than the coturnix. Murray McMurray had BW chicks for sale this year. I've never ordered any from them, but I've ordered chickens, ducks, geese, etc. MM hatchery always compensates with a credit for dead chicks if you let them know within 48 hours. You can also get BW eggs from eBay and Amazon to incubate.