Not sure about your training program--but for me it took only as
long as I was dedicated to study for each test. I knew I needed
General Knowledge, Airbrake and Combination to get the PERMIT so I studied those first
and took one at a time, although I live near the testing (DMV) station.
As I passed each one I'd study for te next and so on until I passed them all.
The three listed above were necessary before starting school--so check with your
community college. Since I had the time I also took tanker, doubles/triples and
haz mat. For Haz you will need to also pay a fee and submit fingerprints for a background
check, which could take 4 weeks.

So to answer your question--get your state testing manual and start studying. There are also
sites online that help you prepare for the tests (see toolbar above--CDL Practice Tests)
I suppose you could get them all in one day if you were to study your butt off.
You won't get your CDL A until you finish school and take your driving test.
The 1st hurdle is to pass your knowledge tests to get your permit!

As I recall the general knowledge was like 50 questions and almost all the others
were like 25 questions. That may differ from state to state.

Good Luck to you!