Though I don’t know exactly what priority review is, in my interview there was definitely strong suggestion to have the application in by early December or late November. The heavy suggestion was because the admissions at Univesity of Rochester look through applications as they come in and the earlier you submit the application, the more likely you are to get some of the scholarship money they have, since they have a limited amount of funds to give out. This is the only advantage I know of for the whole December 1st submission, though I’m sure it is not a solid deadline, and it’s why I submitted on November 26th just to be sure. Hope this helps.