I did the Boeing Everett factory tour last late August, when I was on vacation. I went on a Monday Morning, getting to the tour facility just before 8:30 am. By getting there that early, I was able to get on one of the first tour groups at 9:00 am. The tour lasts just over an hour, includeds a movie on Boeing's history, then a shuttle busse to the massive assembly line, where I saw the 747 line; then back on the bus to across from the assembly building for a ride where they do the painting, final interior and external assembly, testing and delivery (from their own airport there, Payne Field (?)) of the larger aircraft. It is like an international airport of your dreams, with aircraft for airlines from Air France to Vietnam Airlines (both cases included 777's when I was there).
Assuming you have a rental car, you can then spend the rest of the day at the Museum of Flight and Boeing Field. I spent at least 3 hours at the Museum. Boeing Field is also where final prep and delivery of 737 and remaining 757's is done. Go to the websites for the tour and the Museum to find out more info about them. Since you must be a fan of airline aircraft, they it will be well worth the time to visit these places. Seattle itself is a fun place too. You can get a pass good for several days and up to 7 visitor places, including the Space Needle, a 1 hour boat tour of Seattle Harbor, the Aquarium and the Museum of flight for about $40. Check tourist sites for Seattle for more info on that deal. Within Seattle, one should park the car on the outer edge of downtown, and use the busses in the central area which are free during business hours (till 7 pm).