mark cade's book is a good start if you have totally no idea what this exam is for. but so far, no single book can cover the exam 100% (or 80%?) like you may have for
scjp exam. not many good mock exam exist either.
how many days? hard to say, maybe 1-3 months for average guys, depending on your time/expr. the cert itself has no meaning if you only want to cram it in "21 hours".
good luck!