In the Association of American Medical Colleges Guidelines it states that "each school of medicine should prepare and distribute to applicants and college advisors a detailed schedule of its application and acceptance procedures and should adhere to this schedule unledd it is publicly amended."
So, in a nutshell schools only need to abide by their defined dates of notification and acceptance. Some schools give you the dates and are very forthright, but at others you have to search the most remote corners of their websites to find the info.
If you are looking specifically for Mayo's deadline I have no idea 'cause I didn't apply there-sorry.