That depends.
Are you an expert in any language?
Are you an expert in any C family (C, C++, Pascal, etc.) language?
How good are you at sight-checking your source programs so they compile clean the first time?
The JSCP exam is a language lawyer's delight which emphasizes obscure language details and proofreading programs for errors that only a
test constructor would make and only a compiler would find. It tests for Java expertise under time pressure, not just competence.
If you are not yet a Java expert,
you should study a Java
SCJP review book like K&B:
http://www.amazon.com/exec/obidos/ASIN/0072226846/jr%5Fbunk-20/103-7731859-1031869 cover to cover, then do as many mock exams as possible:
http://www.javaranch.com/gramps/SCJPLinks.jsp Early in this process, you'll be able to estimate the time you'll need. The conventional wisdom is that you should be getting over 80% on the mock exams before attempting the real exam.
Good luck!
[ December 28, 2004: Message edited by: Mike Gershman ]