I confirm it was not quick at all.
They started their emergency descent around the Bahrain/Doha area. I estimate their crash to have occurred after 20-25mins.
I doubt a bleed/pack smoke. He stated more then once "we are on fire" which makes me believe he actually had evidence there was fire.
Very important facts if corroborated
It puts a relative time frame on the degradation should a fire have been involved. Also provides a similar time frame if a fuel dump was commanded.
Up until the abandoned landing (as reported) it would be interesting to find out what the track of the aircraft was in the descent.