Brief: That would put current estimates from March 2009 -> September 2010 GRAND OPENING. Assuming Wal-Mart breaks ground in March and the 1 1/2 year estimate above is accurate.
Commentary: After the City of Hillsboro* & Beaverton* both said NO, Cornelius said YES, Please!. I guess the rest of Washington County (Forest Grove*, Sherwood, Tigard, Tualatin, North Plains*, Banks*, Durham, Gaston*, and King City) just weren't appealing to Wal-Mart strategically, because as far as I know development hasn't been proposed there. Nevertheless, I think Wal-Mart will draw from the customer base they're likely targetting, the gold-mine of Hillsboro, Beaverton, and Forest Grove residents. In addition I think people on average of 8 miles or 15 minute drive away from Cornelius, will shop at Wal-Mart. My thought is Beavertonians will refuse the commute and instead continue to bargain hunt at their myriad of shopping malls within reach..K-Mart, Target, WinCo, Cedar Hills crossing, Tanasbourne, and the occasion Washington Square. Of course, the same goes for anyone S/E of them - Sherwood, Tigard, Tualatin, Durham, and King City.
* In my opinion, the most likely residents from which city they'll commute.
Oregonian - Washington County section
Washington County, Oregon Wikipedia