Alwaysinit
The 18-30 rest period was a copy n past extract from CAP371. This was aimed at UK Charter Airlines flying many moons ago UK to initially Orlando day time come back 24 hours later at night. At this time there was only mickey mouse or gospel channels to watch on telly.
Nowadays with the advent of FRMS things have changed a little and the science has moved towards recommending crews to stay as close as possible to their local timezone. This does require a high level of dedication at 0400 US local waiting for breakfast etc. In the case of many flights that EK operate night / day the 18-30 hour rest period is spot on. Short sleep when you arrive, get up , then local nights sleep Dubai time, get up fly home all scientifically validated.
Problem is not all trips are like this and a ULR to Miami and waiting for hours to deplane clear immigration blah blah or ones where its down to one sleep etc are pushing crews to limits never dreamt when Douglas Bader started talking FTL.