Yeah you are correct about the not guaranteed part I almost called them yesterday, but then read that it says not to contact customer service until 5 or more days. My item shipped out last Saturday and is finally going to arrive sometime today.
MAIL CLASS DELIVERY STANDARD CONTACT CUSTOMER SERVICE AFTER:
First-Class Mail® 2 - 3 days (not guaranteed) 5 or more Days from the date of mailing
Priority Mail® 1, 2, or 3 days (not guaranteed) 5 or more Days from the date of mailing
Either way, it is pretty shitty of them to label it as "Priority Mail 2-Day" with a Scheduled Delivery Day: September 3, 2013 on the tracking and yet it doesn't arrive until the 6th. Especially when a signature is required. I am just lucky my roommate is home during the daytime.