Back in bobwhite country, I generally waited until the birds flushed. More fun, more sporting.
In Terlingua, in blue quail country, it's a whole different deal. Blues won't hold a point. You bring a good, trained pointer out here and you better have a dog-psychiatrist on stand-by. Call 'em "run-run birds". Yeah, they'll fly--after they're out of shotgun range.
You take whatever shot you can get. And usually, they're at least 30 yards out when you first see them.