His speed doesn't matter, because it was horizontal. What counts is the vertical acceleration of 32 feet per second per second. This works out to a bit over 6 seconds, ignoring air friction. Call it 7, and you'll probably be pretty close.
Of course, this assumes he flew to 600 feet down, and stopped abruptly. He probably bounced a few times, which would have taken longer.
Damn, that is a long time.