What sounds like a very simple question is actually very complex and there are a number of issues which would contribute to the answer of 'when the crew will actually time out'. It is worth knowing the more often than not, flight crew will 'go out of hours' before the cabin crew (though this may well change when new regulations come into force in February.

Things that come into play are:

Local time of start?
Are crew acclimatised or non acclimatised?
Amount of rest preceeding duty?
Amount of rest down route?
Industrial agreements?
Availability of bunk rest onboard?
Were they called from standby (home or airport)?

Plus a lot more.......

It is possible to extend duties by usin what we refer to a 'discretion'. Again there is a fair amount to consider when exercising this and it is not always possible. Although companies monitor crew hours and more often than not spot issues before they arise, ultimately it is crews responsibility to be aware of their hours and when they are no longer legally allowed to work. The hours we are allowed to fly are set down currently by the CAA and it a legal thing, i.e. We cannot go above what is set down as the maximum. New rules come into force in February which are in line with European regulations, with some exceptions.

Hope this gives some insight.

Regards
D1L

These views are my own and do not reflect those of my employer.