Hi everyone,
I fly the B777 and we've tried the pilot resonse feature enroute, on the long transoceanic segments.
The timing between the different kinds of warnings can be adjusted by the maintenance dept, it is something that an airline can easily adjust.
In my airline the settings are:
20 mins: eicas message "pilot response" and no sound.
25 mins: eicas caution message "pilot resonse" and a caution bleep.
30 mins: eicas warning (red) "pilot response" and a continuous wailer.
It is impossible to sleep through the warning wailer, it is too loud. So I guess that Vietnam airlines have got their settings at more than an hour....