i think that if a print was left in tthe fix too long it would reach a state of equilibrium, it woudn't kill the fix or the print
i have heard .. NEVER seen .. that a print left in fix too long will bleach the print ...
when i was in college students left prints ( rc and fb ) in the fixer for longer than the prescribed time ..
waaaaaay longer .. nothing happened to the print or the fix ...
i think the dude has nothing better to do than be cranky, unless of course
he has noticed problems with his own prints ... then he has reason ,,,
=== added later ===
if it is a shared darkroom maybe the person doesn't want his work thrashed about by others who might not
care for and treat his prints the way he wants them to be treated, so the shorter time in the fix, the better.
i remember gang darkrooms were a nightmare, not only in the fixing tray, but the rotary washer that students loved to
watch spin @ 50 MPH and damage every print in the cage.