For PDT, this is how I told a friend of mine in a similar situation. Graduation was mid December so I told him to send in the application around the beginning of November. It takes about a week till they respond, then about a week or two till the interview. Most classes will start about two to three weeks after the interview. They offered him a class date starting on graduation. He asked if they could put him in the next class since he wanted to walk and parents and all already had made arrangements to attend. No problem, next class was fine with them. Just be honest with them and they will work with you.

Simple...apply about 1.5 months before you want to start.