I know little or nothing about airline operating environments, so can only really comment on what we do in the little aeroplane world - but it might nonetheless be interesting to you.
Generally for a series aeroplane, we'll fly three sorties of testing - typically totalling 2-4 flying hours. These sorties are:-
- A shakedown, normally at moderate weight with minimum crew to check all the main systems are working as advertised. If problems are found, this sortie may be repeated several times until it all works.
- A heavyweight sortie (normally at-least 95% MTOW), ballasted to the furthest forward CG reasonably achievable (which can actually be fairly aft since that's where the cargo/pax go). This will be used for performance checking (particularly climb rates with various safe engine combinations and Vh), and the heavyweight handling - roll rates, pitch authority at low speed, various stalls.
- A lightweight sortie, at the furthest aft CG achievable, this is generally the worst condition for handling so various stalls, extreme attitudes, etc. will be flown as well as usually a check on any known marginal-handling points in a particular envelope. (These schedules are usually standard to type, with maybe a few tweaks introduced by the project FTE according to build standard).
The first two sorties - shakedown and MTOW-fwd may often run into each other since sorting system problems out, if the aircraft has initially been shown "safe to test" can often be slotted into the high weight sortie rather than introducing other single-purpose flights.
One thing I do recall about the big-aeroplane world was a conversation I once overheard with the CTP of Airbus around 1996. He said that he expected each production FTE (and bear in mind they do the majority of the planning and reporting work, not the TP) to clear-through about 18 aircraft per year. That would probably work out at 2-3 weeks work per engineer to clear through each airliner.
In the little aeroplane world, I generally would expect to put around 1-2 weeks in if I'm acting as FTE for the job and it's a straightforward series aeroplane, which seems reasonably proportional since the singles and medium-twins that I work on have rather less complex systems to worry about.
G
N.B. I'm also not a fan of the use of non FT trained pilots in this context, the lack of understanding of flight test reporting in particular. Having said that, mixed TP/operational pilot crews can often work well and save test pilots having to maintain full currency on each type. Also, it is (whatever the ETPS/EPNER Mafia will have you believe) not all that hard to take an able and experienced pilot and train them to do this sort of flight testing - particularly if they are working with an FTE.