Liberty, called Libo at the Academy is never guaranteed, and only begins after each individual cadets Last Military Obligation (called LMO) which can vary by individual. Below is the general guidelines, but like everything at USCGA it is subject to change at any time. Also, if Covid is up in the area, Covid libo rules will be in effect which are even more restrictive.
For Labor day, that is covered under the Holiday Liberty rules, in the Regulations of the Corps of Cadets: After LMO Friday libo may be authorized until 1800 Monday night for a 4/c; upperclassman can return later.
For non holiday weekends:
For a 4/c it usually begins around 1300 on Saturday and ends around 2300 Saturday night.
For a 4/c on Sunday it usually begins at 0730 and ends at 1800.
4/c cadets are not authorized "Shorts" which are Saturday overnights for regular weekends (this does not apply to Federal Holiday weekends like Labor Day.