time

Not a question I can answer accurately. I don't know how fast you read or write or your affinity with the subject. Reading the notes and listening the lectures once probably takes about 24 hours. However the important thing is to do lots of question practice and to critically review your answers. You would probably need to attempt around 10 exams worth of questions to give a good coverage. Say 4 hours each to attempt questions and 2 to study answers, so that's about 60 hours. Total therefore about 80 hours. That's only a very rough calculation.

Is one month enough to prepare only for sbl full time?

If full time, one month should be OK.