Just some clarification needed here.....

There are many Boeing facilities in the Tacoma-Seattle-Everett area.

This also includes the Boeing Museum of Flight---this is not in Everett

http://www.museumofflight.org/

This is located at Boeing Field which is south of downtown Seattle near Boeing field about 7-10 miles north of SEATAC.

The large Boeing manufacturing plant where the 787 is made as up in Everett (actually Mukelteo on Payne Field)

http://www.boeing.com/commercial/tours/index.html

As for the rush hour drive...

From the airport you should be fine until you hit downtown. From the I-90 merge to the University of Washington exit will be heavy.

Same true when you return. The rush hour through downtown seattle starts around 3:30pm.

There is trafic cams that will show you how traffic is of a web site. If you google WSDOT SEattle traffic and
http://www.wsdot.com/traffic/seattle/default.aspx

roughly where 525 and 526 meet is where the Boeing tour location is.