there are no guarantees in the Navy.
My son graduated A school on March 10 2016 (after being told it would be March 11th - it was a last minute change) but he ended up on hold for a couple of weeks afterwards before he was able to fly home on leave. Some of his classmates flew out on the 10th and 11th, some a few days later, I think he was the last to leave or almost so. We didn't know when he would be home until the day before he arrived, if I'm remembering correctly.
He had tickets from A school to his new posting and had to change them to bring him home on leave and then on to his new posting - changing them wasn't an issue - he just had to pay the difference.