What would everyone consider an acceptable layover time for the ULR trips ? And why ?
You must be from EK mismanagment!!!!!!!!!!
A simple search on pprune (try fatigue....) or even on google will lead you to many scientific research from the highest competent bodies. Just start with the one from NASA and finish with some findings of the NTSB.
But as always the morons from EK think they know better and start their own new invention of the wheel. Needless to say they end up with a camel hump and in a sectarian self induction become even proud of it.
The basic answer to your question is.....
After a ULR duty:
It takes at least two sleep cycles to get adequate rest to be fit for duty. It takes three regular meals to bring the stomach into synch. It takes a quiet environement for the sleep rest. It takes a possibilty for a adequate hot meal at any time during rest (see above). It takes horizontal AND upright and seated rest periods on a return ULR-flight. It takes a normal work atmosphere to counteract adequately fatigue related concentration symptoms during business hours (this means that your work environement should not be compromised by others resting, chatting or eating behind your back). ULR flights should not be prone to overduty and such overduty must be strictly limited by regulation and this limit must be strictly enforced (a guideline is 10% of block maximum).
Now put this into a regular IAH or future LAX flight and you can see that EK scratches almost each and every well researched and founded finding right from the outline.
Guys from the mismanagement:
Do never come back with such stupid questions again, it's only exposing your blatant incompetence and complete disregard of basic human factors.
Go enjoy the beach .....