Split crew rest on Qatar Airways Airbus 350
I was wondering if having a split rest on QR A350 flights to US and Australia is legal. Namely, Qatar Airways Airbus A350 has a crew complement of 13 members but only 6 bunks for rest. That makes 2 groups of 6 crew have a 3 hours rest, while one crew member has a split rest - 90 minutes immediately after take off and 90 mins before landing. I'm somewhat convinced that the rest should be at least 3 hours in one block, not split. Which body and which document governs maximum flying time and in-flight rest? Does the QCAA has ultimate authority and freedom on making these regulations or it has to follow ICAO guidelines? If so, where can these ICAO guidelines be found?