I had a couple friends looking at doing the same thing at PDT. I told them to apply about four to six weeks before graduation. Figure it will take a little bit of time to set up an interview (1-2 weeks) then, assuming a job offer is extended (which at PDT you will know before you leave) another 1 to 2 weeks. Both my friends had a class date starting the day of graduation so they asked to start in the following class and that was ok but from what I have heard they want people who can start ASAP. Good luck!