3 months is enough for most people. i'm not most people so i started studying a lot in advance. of course I didn't take it seriously until about 2 months before... so i guess you can get away with starting 3 months before. anyway, PR materials are good, as are examkrackers (for the 1001 series, i haven't used the science books by them before so I can't vouch).
well you'll hear this a million times, but make sure you get a lot of practice. cheers