The definitive answer from NW:

Dear UpgradeMe,

Thank you for contacting Northwest Airlines.

A connection is a flight segment connecting to another flight segment
the same day. Per the rules, the LAX/DEN/LAX must make up the entire
itinerary to qualify for bonus mileage.

Thank you for choosing Northwest/KLM Airlines. We appreciate your
business.

Sincerely,

Susan Curtis
Executive Assistant

Original Message Follows:
-------------------------

Ms. Curtis:

Please do me the courtesy of defining a "connection" for purposes of the

LAXDEN promo. Is it two hours? Four hours? Six hours? Any onward
flight the
same day? Some other definition?

Thank you.

UpgradeMe