It means that for AF447 flight, with cruise altitude of about 10700 meters, the duration of coming down was less than 3 minutes.
The duration of coming down for the wreakage of the midair over lake constance was a little over 2 minutes, so that would be the number for a total desintegration. Stalled/spinning would be a little more, a dive a little less. so we are talking about 1-3 Minutes from cruise to impact.