I'd like to buy a model in alumide now that the design requirements have changed and polished alumide is available, however... The design page says it takes 10 working days (ship by May 18). The shopping cart is telling me that it takes 13 (May 23). What's up with that? I'm on a deadline and those 4 days would make the difference between shipping with enough time and not shipping until the day of the deadline. Is there some holiday factored in there?