i know this is an old post but i need to know this.To the previous poster those birds are nowhere near full grown. Coturnix reach sexual maturity around 2 months old and aren't fully grown out for another couple months.
At 5-6 weeks you are going to feel like you wasted time an money butchering them. There is some meat on them but an average rule of thumb for cots is that carcass weight is about half of live weight.
With coturnix there is also a big misconception that 8 weeks is fully mature. That came from studies done on the growth curve of quail (all livestock has a growth curve) basically at 8 weeks the growth curve has reached its peak meaning any more weight gained comes at a loss of dollars due to feed cost. If you aren't selling carcasses or tight on money you can disregard that rule. I personally butcher closer to 12 weeks. A 12 week old bird is substantially larger than an 8 week old bird and Im in it for the meat so I always go to at least 10 weeks.