Ive always found its not the distance your bird will fly, its the speed at which she comes to you will tell you when she is ready to fly loose. If she is flying, say 50 yards the second you whistle without hesitation, then introduce her to the lure and fly her free. If she is looking, and thinking about it then she aint ready to fly free.
My last harris i took from the aviary and was flying free in a record time of 4 days. The first time a flew one i spent weeks before plucking up the courage to let her loose. Its a BIG step ( one of three) and the first time you do it every possible scenari