Beyond simply sharing with you that you cannot complete the divemaster course in three days, I'd like to add to the prior posts by first encouraging you to go forward with a DM program, but with a different attitude. Look at the program not as something to complete, but as something to grow you into being a competent dive professional. Entering the professional ranks, it is (or should be) about competence, experience and maturity. Presently, if your profile is up to date, you lack enough dives to be a divemaster, though you can start the program. Rather than getting "irrelevant" specialties (I think people should do those in areas of personal interest- photography, ecology, etc) I think you need to focus on getting more bottom time, perhaps in different conditions and venues, if possible. Dive with experienced divers, and grow yourself as a diver on every dive. The basic open water skills you will assist in teaching must be honed by you to be demonstration quality. That is not learned in a classroom. Also, as a DM leading recreational divers, you need to have as second nature excellent buoyancy skills, be efficient in you use of air so you are not having to end a dive for paying customers because you are the first to be low on air, and also, recognition and correction of problems other divers are having even if they don't have a full awareness themselves. That takes time and that takes more than 15 days, even of intense training. So be prepared to grow into being a Dive Master. I for one think it is a huge deal to have that title and to know what it means. It is an even bigger deal to DO what divemasters do, and do it well. So work hard, be diligent, and I am confident you will become a terrific divemaster. Plus, you get to wear the cool shirts and hats!
DivemasterDennis