http://www.usna.edu/AdminSupport/_files/documents/instructions/5000-5999/5720.1N.pdf
This may not be the most current version, but I suspect it is still limited to 1/c and 2/c, with 3/c in critical areas. This is the program run by Admissions that allows mids to depart early to go home and speak in high schools in their area, as recruiting needs dictate.
To answer the original question, Thanksgiving leave, the class day starts extra early on Wednesday before Thanksgiving, squeezing all 5 periods of the academic day in before noon. Once academic classes are done for your mid, and any other required events or any required sign-out performed, they are free to go. Depending on what time liberty is secured (vacation officially over) on Sunday night, mids traveling by plane must schedule their flight to land a specified number of hours before that report back no later than time.
Caveat: This is the way it has been done for many years. There is always the chance for tweaks. I have watched the Sunday return time vary among 6, 8 and 10 pm over the years. If the "nose count" that night is particularly painful, and people (Commandant's staff) are up after midnight trying to get an accurate count of who's back and who's not and why and where are they - the next year it's back to 6 pm.
Tough on West Coasters who have to change planes when connecting from a region airport. Sunday is essentially lost as a travel day. Many families change it up and take the family east to visit friend or relatives, easing the trip on the mid to something shorter, allowing more time together. NYC is a popular meet-up. We usually have several mids here at the house, whose finances don't permit a Thanksgiving trip home and then winter break trip a month later.