Well that's interesting. Thanks to vmandr and the Hellenic CAA press release, we now know that Athinai ACC was calling 804, on en-route and emergency frequencies, without response, for 2 minutes and 40 seconds before "the flight signal was lost from radar".
What do we make of that?
But the last definite radio contact with the aircraft was at 02:48. Therefore, there's in fact 40 odd minutes unaccounted for before it went down.