How long will it be til I get my DEP Discharge Letter? ?

I was in the Marines D.E.P. for a couple of months and I was suppose to ship off on October 20th, 2008.. They offered me a really good job but it wasn't something I wanted to do with my life. I later found out that the Air Force has the job I want to go for and I already have my ociates degree for that field.. I then talked to my Marines recruiter and told him about the situation and surprisingly he was ok with it.. of course he tried to talk me out of it but he wasn't too harsh cuz we knew each other for awhile anyway.. Unfortunately, I cannot join the Air Force until I receive the DEP Discharge letter and now my old Marines Recruiter is telling me that it can take up to 6 months. Why is that?