Hmmmmm--- Did you keep a copy of both flight plans? Were there noticeable differences in times between waypoints? Could you identify where they and shaved off that much time? If so, it sounds like the perfect opportunity to write a NASA safety report, and include copies of the two flight plans. I would also send a copy of everything to ALPA's safety and contract enforcement offices.
It is a violation of the FAR's for a dispatcher to knowingly send you a flight plan with erroneous data in it. And if there are gross differences in times between waypoints, that would be pretty solid evidence of malfeasance.
Of course, by accepting a flight plan that you know had bogus numbers in it, you may be putting yourself on report also, if you submit the NASA report.
The only way we can stop this kind of nonsense is to write it up and get it on the record.
It hasn't happened to me yet, but I'm sure it is only a matter of time, if guys don't step up and report this kind of Cr_p.