Portland is 2 hours behind Mexico City
Best overlap: 10:00 AM to 6:00 PM in Mexico City is 8:00 AM to 4:00 PM in Portland.
For the smoothest call, aim inside 10:00 AM to 6:00 PM in Mexico City, i.e. 8:00 AM to 4:00 PM in Portland. That's a roomy 8 hours of common time each day, so finding a slot that suits everyone is rarely a problem. Seasonal note: Portland uses daylight saving and Mexico City doesn't, so double-check the times in your own months — they can move by an hour.