Also, don't forget that...
... at any point during an ULH flight, two of the four flight crew;
- still have to go on the first break,
- still have to plan to be fresh for the landing,
- must be alert enough to soundly manage enroute contingencies,
- still have to plan ahead for eating/hydrating throughout the journey, and
- all must deal with the vagaries of different abilities to 'sleep' in a M0.86 tube in the sky!
Keg is correct. In my experience it will not make sense to mandate any such 'narrow' pre-flight criteria. Pilots know their own limits & responsibility for 'rest preparedness' to fly. They also know the CAOs.
I hope it's left at that unless EVIDENCE proves that systemic abuse of those responsibilities is occurring.👌