i was wondering about that too. i fix for 10 to 12 minutes in 1+4 ilford rapid fix. no pink cast on the negs after this and using hypo clearing agent and a nice washing.
Is this fixing time too long, what would be the consequences of "overfixing"? I developed a lot of trix lately with this fixing and everything seems to work just fine.

EDIT: I#m speaking of 35mm film. But it does not seem to be all to different