You already have
SCJP and SCWCD, so you know how these exams work. SCBCD is not much different. I'd say four weeks should be enough if you are determined, even less if you know something about the subject.
Of course Hebert has the point here: only you and mocks can tell how close you are to achieving the goal.
SCJP5, SCWCD5, SCBCD5, Oracle SQL Expert