Forcing someone to go over duty time could be construed as a criminal act. There is, however, a lot of subtle and not so subtle pressure from some unscrupulous operators to get the job done in a shorter time than is possible and thus duty time is exceeded.
At the end of the day, the only one who'll be caught under the hammer is the pilot so folding and going with the flow can be self defeating. It's not an easy thing to do but sometimes it's better to turn down something that is blatantly wrong.
You've uncovered a minefield here.......
