Great question! 

While most of the time we get to the orders as soon as they come in, we still have to allow one day for processing the part here at Rivers Edge.  This generally means that the order will be processed by UPS the following day.  Two day shipping means two business days, which excludes weekends and other events that can occur.  Please check out UPS for more information.  http://www.ups.com/content/us/en/resources/service/common_questions.html#Why+wasn%27t+my+package+delivered+in+three+days%2C+as+indicated%3F