I had a ticket to BUD from MSP on Thanksgiving day, and NW cxld their last flight at 21:15, putting me on the 18:00 flight instead.
HERE IS THE RULE:
If it's more than a 3-hour change on departure or arrival, NW will change the ticket or refund the entire amount, for no fee.
Because yours is just under 3 hours, NW is still reasonably accommodating you, according to the NW contract of carriage (I remember doing a search when trying to cancel mine, and the rule specifically states 3 HOURS).
That doesn't mean it's fair, but at least you understand if you keep getting the same answer.
Good luck anyway!