There are two ways:
Method 1: The easiest way is to go to my photostream and you will find the newest uploads begin at the top of page 1. The uploads get older as the page numbers get higher with the oldest uploads on the last page.
Method 2: Open one of the Yearbooks sets (A through Z) and you will find the newest uploads at the end/bottom of the set. (The oldest uploads appear at the beginning/top of the set.)
By the way, the contents of the A through Z sets are organized according to school name, for example, the photos from Hard Knox High School would be in the Yearbooks H set.