I don't want to dominate Joe's thread but I'll respond. Joe can chime in and agree or disagree.

Traditional hacking has been going on for hundreds of years. Woodford, in A manual of falconry states the traditional wisdom regarding when to take a bird up:

"When, after three or four weeks, usually less in enclosed country, a hawk is observed to have failed to turn up at feeding time more often than once- especially if the two absences are consecutive - it is time to catch it up."

So one kill doesn't necessarily end the hack. Regularly being able to provide for himself does.

Also Jeff: I hope I didn't sound negative about the 15 day thing. I didn't mean to. Some people prefer later taken chicks. It's a trade-off in regards to behavior.