Specialty boards and the RRC stipulate the requirements for training, including the maximum amount of time allowed off per year of training.
It is your program director's responsibility to see that you meet the requirements for board eligibility. In addition, there may be institutional policies in place but in general, it is up to each specialty program director to determine allowable vacation time (meeting board requirements for training of course) and how that is allocated.
aPD can address this but I cannot find any documentation that ACGME is responsible for protecting that time. As noted above, your contract should stipulate that and is generally managed by the graduate medical education office.