I think they were still pretty close together as Discovery was still doing the ISS flyaround. A great sight wasn't it...
According to
http://www.nasa.gov/returntoflight/c..._timeline.html
Saturday, August 6 (Flight Day 12):
12:24 a.m. Discovery/ISS crew farewell and hatch closure
3:22 a.m. Discovery/ISS undocking
3:52 a.m. Discovery flyaround of ISS
5:05 a.m. Final separation from ISS
9:30 a.m. Mission status briefing (flight control team video replay follows)
The Melbourne flyover occured at 4:37am Eastern USA time therefore - 45mins into the ISS flyaround and 28mins before the final burn to seperate Discovery and ISS.