I wouldn't consider the tour a part of the interview (it is optional), but on the other hand I wouldn't go doing anything that might make the chief pilot remember you for the worse.
On the day of my tour (a Tuesday), a large group of employees were having a luau in the building. Hawaiian shirts, lei's, fake palm trees, the works. Of course they got a big kick out of pointing out how out of uniform we were in our interview suits!
Don't miss the tour. It's a great opportunity to get more of a feel for the company, and to ask any questions you might have.
T1bubba